Pharmacokinetics of Theophylline and It's N-7 Derivatives in Rabbits

Home , Aminophylline, Proxyphylline

AN ABSTRACT OF THE THESIS OF

WATTANAPORN TAVIPATANA for the degree of Master of Science in Pharmacy presented on April 30, 1984.

Title: Pharmacokinetics of Theophylline and its N-7

Derivatives in Rabbits Redacted for Privacy Abstract approved: Dr. Jamey r. Ayres

Pharmacokinetics of theophylline and N-7 substituted

theophylline in rabbits when administered alone and in

various combinations were investigated. This thesis has four chapters dealing with etophylline and theophylline;

proxyphylline and theophylline; dyphylline and theophylline;

and etophylline, proxyphylline and dyphylline phar-

macokinetics when administered concomitantly. All chapters

are interrelated. Each chapter has its own abstract. PHARMACOKINETICS OF THEOPHYLLINE

AND IT'S N-7 DERIVATIVES

IN RABBITS

Wattanaporn Tavipatana

A THESIS

Submitted to

Oregon State University

in partial fulfillment of

the requirements for the

degree of

Master of Science

Completed April 30, 1984

Commencement June 1984 APPROVED: Redacted for Privacy Proffeissor of Pharmdci /In Charge of Major Redacted for Privacy Deah of College of Pharmacy Redacted for Privacy

Dean of bcnool

Date thesis is presented April 30, 1984

Typed by Elaine Plaggert for Wattanaporn Tavipatana ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. J. W. Ayres for his friendliness, patience, encouragement and constant guidance throughout my research work.

I wish to express my sincere appreciation to Dr. J. M.

Christensen and Dr. D. Thomas for their suggestions and advice.

I am deeply gratejul to my parents for their never ending love, encouragement and financial support.

My special thanks to Mike Cole for his valuable assistance. TABLE OF CONTENTS

CHAPTER I: ETOPHYLLINE AND THEOPHYLLINE 1 PHARMACOKINETICS WHEN ADMINISTERED CONCOMITANTLY

ABSTRACT 2

INTRODUCTION 3

MATERIALS AND METHODS 6

RESULTS AND DISCUSSION 10

CONCLUSION 34

ENDNOTES 35

REFERENCES 37

CHAPTER II: PROXYPHYLLINE AND THEOPHYLLINE 40 PHARMACOKINETICS WHEN ADMINISTERED CONCOMITANTLY

ABSTRACT 41

INTRODUCTION 43 MATERIALS AND METHODS 46

RESULTS AND DISCUSSION 48

CONCLUSION 69

ENDNOTES 70

REFERENCES 71

CHAPTER III: DYPHYLLINE AND THEOPHYLLINE 73 PHARMACOKINETICS WHEN ADMINISTERED CONCOMITANTLY

ABSTRACT 74

INTRODUCTION 76 MATERIALS AND METHODS 79

RESULTS AND DISCUSSION 81

CONCLUSION 103

ENDNOTES 104

REFERENCES 105

CHAPTER IV: ETOPHYLLINE, PROXYPHYLLINE AND 108 DYPHYLLINE PHARMACOKINETICS WHEN ADMINISTERED CONCOMITANTLY

ABSTRACT 109

INTRODUCTION 111 MATERIALS AND METHODS 114

RESULTS AND DISCUSSION 117

CONCLUSION 154

ENDNOTES 155

REFERENCES 156

BIBLIOGRAPHY 158

APPENDICES 161 LIST OF FIGURES

Figure Page

I.1 Plasma concentraton time curves for 11 theophyline after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits.

I. 2a Plasma concentration time curves for 12 theophylline after administration of aminophylline (40 mg/kg intravenous infusin over 30 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

I.2b Plasma concentration time curves for 13 etophylline after administration of aminophylline (40 mg/kg intravenous infusin over 30 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

I .3a Plasma concentration time curves for 14 etophylline after administration of etophylline (150 mg/kg intravenous infusin over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in rabbits.

I.3b Plasma concentration time curves for 15 theophylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits.

1.4 Plasma concentration time curves for 16 theophylline fitted by a two compartment open model after administration of aminophylline (40 mg/kg intravenous infusin over 30 minutes) in Subject D. Figure Page

1.5 Plasma concentration time curves for 17 theophylline (*) and etophylline (*) after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in subject Q.

1.6 Plasma concentration time curves for 18 theophylline (m) fitted by a two compartment open model and etophylline (*) fitted by a three compartment open model after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in subject T.

1.7 Plasma concentration time curves for 27 etophylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) in 6 rabbits.

1.8 Etophylline plasma concentration time 28 curve fitted by a two compartment open model after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) in subject S.

1.9 Etophylline plasma concentration time 29 curve fitted by a three compartment open model after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) in subject EE.

II.la Plasma concentration time curves for 49 theophylline after adminstration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. Figure Page

II.lb Plasma concentration time curves for 50 proxyphylline after adminstration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) and proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

II.2a Plasma concentration time curves for 51 proxyphylline after adminstration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits.

II.2b Plasma concentration time curves for 52 theophylline after adminstration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits.

11.3 Plasma concentration time curves for 53 theophylline (0) and proxyphylline (0) after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr over 2 hours) in subject BE.

11.4 Typical plasma concentration time 54 curves for theophylline (0) and proxyphylline (0) after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in subject HH.

11.5 Plasma concentration time curves for 60 proxyphylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) in 6 rabbits. Figure Page

11.6 Typical plasma concentration time 62 curve for proxyphylline after administering proxyphylline (135 mg/kg by intravenous infusion over 5 min) in subject RR.

III.la Plasma concentration time curves for 82 theophylline after admininstration of aminophylline (40 mg/kg intravenous infusion over 30 min) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 min) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hrs) in 6 rabbits.

III.lb Plasma concentration time curves for 83 dyphylline after administration of aminophylline (40 mg/kg intravenous infusion over 30 min) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 min) and dyphylline maintenance dose (100 mg/kg/hr over 2 hrs) in 6 rabbits.

III.2a Plasma concentration time curves for 84 dyphylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in 6 rabbits.

III.2b Plasma concentration time curves for 85 theophylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in 6 rabbits.

III .3 Plasma concentration time curves for 86 theophylline (0) and dyphylline (V) after administration of aminophyline (40 mg/kg intravenous infusion over 30 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in subject UU. Figure Page

111.4 Typical plasma concentration time 87 curves for theophyline (0) and dyphylline (7) after administration of dypylline (300 mg/kg intravenous infusion over 8 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in subject W.

111.5 Plasma concentration time curves for 94 dyphylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 minutes) in 6 rabbits.

11.1.6 Typical plasma concentration time 95 curve for dyphylline after administering dyphyline by intravenous infusion over 8 min) in subject Z.

IV.la Plasma concentration time curves for 118 etophylline after administering etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

IV.lb Plasma concentration time curves for 119 proxyphylline after administering etophyline (150 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

IV. 2 Typical plasma concentration time 120 curves for etophylline (*) and proxyphyline after administering etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours). Figure Page

IV. 3a Plasma concentration time curves for 121 proxyphylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 4 rabbits.

IV. 3b Plasma concentration time curves for 122 etophylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 4 rabbits.

IV. 4 Typical plasma concentration time 123 curves for proxyphylline (0) and etophylline (*) after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) and etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in subject GG.

IV. 5a Plasma concentration time curves for 124 etophylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

IV.5b Plasma concentration time curves for 125 dyphylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. Figure Page

IV.6 Typical plasma concentration time 126 curves for etophylline (*) and dyphylline (V) after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in subject XX.

IV. 7a Plasma concentration time curves for 127 dyphylline after administering dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

IV.7b Plasma concentration time curves for 128 etophylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

IV. 8 Typical plasma concentration time 129 curves for dyphylline (7) and etophylline (*) after administering dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in subject X.

IV. 9a Plasma concentration time curves for 130 proxyphylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in 4 rabbits. Figure Page

IV. 9b Plasma concentration time curves for 131 dyphylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in 4 rabbits.

IV.10 Typical plasma concentration time 132 curves for proxyphylline (0) and dyphylline (V) after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) and dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in subject YY.

IV.11a Plasma concentration time curves for 133 dyphylline after administering dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

IV.11b Plasma concentration time curves for 134 proxyphylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits.

IV.12 Typical plasma concentration time 135 curves for dyphylline (7) and proxyphylline (6) after administration of dyphylline (300 mg/kg intravenous infusion over 8 minutes) and proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in subject Z. LIST OF TABLES

Table Page

I.1 Pharmacokinetic parameters for 19 aminophylline after administering aminophylline (40 mg/kg intravenously over 30 min) in rabbits.

I.2a Pharmacokinetic parameters for 20 theophylline after administering aminophylline (40 mg/kg intravenously over 30 min) followed byetophylline (150 mg/kg intravenously over 5 min and 30 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

I.2b Pharmacokinetic parameters for 21 etophylline after administering aminophylline (40 mg/kg intravenously over 30 min) followed byetophylline (150 mg/kg intravenously over 5 min and 30 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

I. 3a Pharmacokinetic parameters for 22 etophylline following two compartment open model after administering etophylline (150 mg/kg intravenously over 5 min) followed byaminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits.

I.3b Pharmacokinetic parameters for 23 etophylline following three compartment open model afteradministering etophylline (150 mg/kg intravenously over 5 min) followed byaminophylline (40 mg/kg intravenous infusion over30 min) in rabbits.

I. 3c Pharmacokinetic parameters for 24 theophylline after administering etophylline (150 mg/kg intravenously over 5 min) followed byaminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits. Table Page

I. 4a Pharmacokinetic parameters for 30 etophylline following two compartment open model after administering etophylline (150 mg/kg intravenously over 5 min) in rabbits.

I.4b Pharmacokinetic parameters for 31 etophylline following three compartment open model after administering etophylline (150 mg/kg intravenously over 5 min) in rabbits.

Pharmacokinetic parameters for 55 theophylline following one compartment open model behavior after administering aminophylline (40 mg/kg intravenous infusion over 30 min) followed by proxyphylline (135 mg/kg loading dose intravenous infusion over 5 min and 15 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits

II.lb Pharmacokinetic parameters for 56 theophylline following two compartment open model behavior after administering aminophylline (40 mg/kg intravenous infusion over 30 min) followed by proxyphylline (135 mg/kg loading dose intravenous infusion over 5 min and 15 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits

II.2a Pharmacokinetic parameters for theo- 58 phylline following one compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits.

II.2b Pharmacokinetic parameters for theo- 59 phylline following two compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits. Table Page

II.3a Pharmacokinetic parameters for 63 proxyphylline following two compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) in rabbits.

II . 3b Pharmacokinetic parameters for 64 proxyphylline following three compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) in rabbits.

II. 4a Pharmacokinetic parameters for 65 proxyphylline following two compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits.

II . 4b Pharmacokinetic parameters for 66 proxyphylline following three compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits.

11.5 Pharmacokinetic parameters for proxy- 67 phylline after administering aminophylline (40 mg/kg intravenous infusion over 30 min) followed by proxyphylline (135 mg/kg loading dose intravenously over 5 min and 15 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

III.la Pharmacokinetic parameters for theo- 88 phylline following one compartment open model behavior afteradministering aminophylline (40 mg/kg intravenous infusion over 30 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits. Table Page

III.lb Pharmacokinetic parameters for theo- 89 phylline following two compartment open model behavior after administering aminophylline (40 mg/kg intravenous infusion over 30 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

III.2a Pharmacokinetic parameters for theo- 90 phylline following one compartment open model behavior after administering dyphylline (300 mg/kg intravenous over 8 min) followed by aminophylline (40 mg/kg loading dose intravenously over 30 min) in rabbits.

III.2b Pharmacokinetic parameters for theo- 91 phylline following two compartment open model behavior afteradministering dyphylline (300 mg/kg intravenous over 8 min) followed by aminophylline (40 mg/kg loading dose intravenously over 30 min) in rabbits.

III.3a Pharmacokinetic parameters for 97 dyphylline following two compartment open model behavior afteradministering dyphylline (300 mg/kg intravenous infusion over 8 min) in rabbits

III.3b Pharmacokinetic parameters for 98 dyphylline following three compartment open model behavior afteradministering dyphylline (300 mg/kg intravenous infusion over 8 min) in rabbits

III.4a Pharmacokinetic parameters for 99 dyphylline following two compartment open model behavior afteradministering dyphylline (300 mg/kg intravenous infusion over 8 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits. Table Page

III.4b Pharmacokinetic parameters for 100 dyphylline following three compartment open model behavior after administering dyphylline (300 mg/kg intravenous infusion over 8 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in rabbits.

111.5 Pharmacokinetic parameters for 101 dyphylline after administering aminophylline (40 mg/kg intravenous infusion over 30 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV. la Pharmacokinetic parameters for 136 etophylline following two compartment open model behavior afteradministering etophylline (150 mg/kg intravenous infusion over 5 min) followed by proxyphylline (135 mg/kg loading dose intravenously over 5 min and 15 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV.lb Pharmacokinetic parameters for 137 etophylline following three compartment open model behavior afteradministering etophylline (150 mg/kg intravenous infusion over 5 min) followed by proxyphylline (135 mg/kg loading dose intravenously over 5 min and 15 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV. 2 Pharmacokinetic parameters for 138 proxyphylline after administering etophylline (150 mg/kg intravenous infusion over 5 min) followed by proxyphylline (135 mg/kg loading dose intravenously over 5 min and proxyphylline maintenance dose by intravenous infusion over 2 hours) in rabbits. Table Page

IV. 3a Pharmacokinetic parameters for 139 etophylline following two compartment open model behavior after administering etophylline (150 mg/kg intravenous infusion over 5 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV. 3b Pharmacokinetic parameters for 140 etophylline following three compartment open model behavior afteradministering etophylline (150 mg/kg intravenous infusion over 5 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV. 4 Pharmacokinetic parameters for 141 dyphylline after administering etophylline (150 mg/kg intravenous infusion over 5 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV.5 Pharmacokinetic parameters for proxy- 142 phylline following two compartment open model behavior afteradministering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by etophylline (150 mg/kg loading dose intravenously over 5 min and 50 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV.6 Pharmacokinetic parameters for 143 etophylline (135 mg/kg intravenous infusion over 5 min) followed by etophylline (150 mg/kg loading dose intravenously over 5 min and 30 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits. Table Page

IV. 7 Pharmacokinetic parameters for proxy- 144 phylline following two compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV. 8 Pharmacokinetic parameters for proxy- 145 phylline following three compartment open model behavior after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV. 9 Pharmacokinetic parameters for 146 dyphylline after administering proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by dyphylline (300 mg/kg loading dose intravenously over 8 min and 100 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV.10a Pharmacokinetic parameters for 147 dyphylline following two compartment open model behavior after administering dyphylline (300 mg/kg intravenous infusion over 8 min) followed by etophylline (135 mg/kg loading dose intravenously over 5 min and 30 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV.10b Pharmacokinetic parameters for 148 dyphylline following three compartment open model behavior after administering dyphylline (300 mg/kg intravenous infusion over 8 min) followed by etophylline (135 mg/kg loading dose intravenously over 5 min and 30 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits. Table Page

IV.11 Pharmacokinetic parameters for 149 etophylline after administering dyphylline (300 mg/kg intravenous infusion over 5 min) followed by etophylline (150 mg/kg loading dose intravenously over 5 min and 30 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV.12 Pharmacokinetic parameters for 150 dyphylline following two compartment open model behavior after administering dyphylline (300 mg/kg intravenous infusion over 8 min) followed by proxyphylline(135 mg/kg loading dose intravenously over 5 min and 15 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits.

IV.13 Pharmacokinetic parameters for proxy- 151 phylline after administering dyphylline (135 mg/kg intravenous infusion over 8 min) followed by proxyphylline (135 mg/kg loading dose intravenously over 5 min and 15 mg/kg/hr maintenance dose by intravenous infusion over 2 hours) in rabbits. PHARMACOKINETICS OF THEOPHYLLINE AND

IT'S N-7 DERIVATIVES IN RABBITS

CHAPTER I

ETOPHYLLINE AND THEOPHYLLINE PHARMACOKINETICS

WHEN ADMINISTERED CONCOMITANTLY 2

ABSTRACT

Etophylline and theophylline were given alone and concomitantly to rabbits. Theophylline plasma concentration time curves were well described by a two compartment open pharmacokinetic model with mean half-lives of 5.2, 4.8, and

5.8 hr when administered alone, followed by etophylline, and following etophylline, respectively. Mean Vd values were 0.706, 0.556 and 0.704 L/kg respectively. Plasma concentration data for bolus etophylline were fitted by a two compartment open model for some subjects and a three compartment open model for others. Mean half-lives were 1.75 hr with mean Vd of 1.1 L/kg for etophylline alone and2.0 hr (two compartment) or 3.0 hr (three compartment) with mean Vd of 1.25 and 1.46 L/kg, respectively,when followed by aminophylline. Etophylline given as a bolus loading dose with an infusion maintenance dose in the presenceof aminophylline had a mean half-life of 2.2 hr. Overall, analysis of variance and Kruskal-Wallis test showed that differences among and Vd for etophylline or for theophylline in the different treatments were not statistically significant at a = 0.05. 3

INTRODUCTION

Theophylline has been widely used in treatment of asthmatic patients since 1937. Because of its poor water solubility and high toxicity, many salts and derivatives have

been developed. One salt is aminophylline, the ethylenediamine salt of theophylline, which was developed in 1908

because it had improved water solubility compared to

theophylline. Among the derivatives of theophylline is etophylline (8-hydroxyethyltheophylline) which was intro-

duced in 1951 (1). The effectiveness of theophylline and its toxicity are

related to plasma concentration (2). Its narrow therapeutic window (10-20 ug/m1) causes complications in admi-

nistration of the drug in emergency situations. Intravenous doses of aminophylline given too rapidly causes

adverse effects in the central nervous, cardiovascular, and

respiratory systems (3). Allergic reactions, aminophylline poisoning, and sudden deaths associated with rapid intrave-

nous injections have been reported (4). Etophylline is a N-7 substituted theophylline deriva-

tive which is an effective bronchospasmolytic agent (5). Etophylline does not release theophylline in vitro or in

vivo and has its own pharmacokinetic and pharmacodynamic 4 properties. Etophylline has a shorter half-life and is eliminated more rapidly than theophylline. It is metabolized and only 20% is eliminated unchanged by the kidneys in humans. It has been widely used in many countries, especially in Germany in the treatment of asthma as a bronchodilator (6). It is available in many trade preparations alone and in combinations (7,8), including a theophylline and etophylline complex (8). Etophylline is reported to be 0.14 times as potent as theophylline in producing bronchorelaxation on rat tracheas (9). Complete pharmacodynamics of etophylline are still not known, but it is believed to have lower toxicity than theophylline. Aminophylline should not be given concurrently with other xanthine preparations (3), presumably because of potentially synergistic toxicities. Etophylline is for- mulated with theophylline (8) but a literature search failed to reveal any reports of concomitant toxicities or pharmacokinetics. In emergency cases in countries where etophylline is used, it may be desirable to rapidly administer etophylline to patients who are currently receiving theophylline or theophylline salts. Etophylline might even replace aminophylline for intravenous administration if it is safe and effective when given as an intravenous bolus to patients who have been taking theophylline. These patients already have a partial "theophylline load" and should only receive adjusted doses of aminophylline infused over 20 5 minutes (10). This study was undertaken to investigate the pharmacokinetic behavior and gross toxicity of theophylline and etophylline when given alone and concomitantly in rabbits. 6

MATERIALS AND METHODS

Female New Zealand white rabbits weighing 1.90-3.13 kg were used in this study. Six rabbits received each treatment, without cross-over. Any rabbits which received both treatments had an elapsed time of at least two weeks between treatments. Rabbits were restrained with a cloth body cloak with safety pins. The hair on both ears was shaved and the ears cleaned with warm water and then with alcohol.1 The rabbit was placed on a heating pad and lidocaine2 was injected subcutaneously close to an ear vein or artery for local anesthesia prior to catheterization. On one ear a Quik-Catho3 26 Ga was inserted into the outer marginal ear vein for drug infusion. On the other ear a

Quik -Cath® 22 Ga was inserted into the mid ear artery for collection of blood samples. Catheters were closed with infusion plugs.4

Etophylline5 was dissolved in D -5 -W6 (dextrose 5% in water) and filtered? (2 microns) and diluted with D-5-W when used. Aminophylline8 was diluted with D-5-W to a desired concentration. Drugs were injected into the ear vein through the infusion plug using a laboratory infusion pump9 or hospital IV pump. 10

Arterialblood samples were collected through the 7 infusion plug using a needle (21 G lf)11 which had been con- nected to 12 inches of heparin washed intramedic polyethylene tubing PE 90.12 Blood was allowed to flow freely after the needle penetrated the infusion plug of the arterial catheter. About 300 ul of the first blood collected was discarded and then about 300 ul was collected in a 500 pl heparinized micro centrifuge tube.13 200 ul of 20 units/ml of heparin14 in D-5-W was injected into the infusion plug prior to and after each blood sample collection. Samples were collected at 10, 20, 30, 45 and 60 min., 2,3, 4,5, 6,

8, 10 and 12 hrs.

Drug Administration Treatments

Treatment 1: Aminophylline (40 mg/kg, equivalent to 31.58 mg/kg of theophylline on a molecular weight basis) was diluted with D-5-W to 6.3 ml and was administered by intravenous infusion at the rate of 0.21 ml/min over 30 min.

Treatment 2: 150 mg/kg of etophylline (50 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min.

Treatment 3: 40 mg/kg in 6.3 ml of aminophylline was administered by intravenous infusion at the rate of 0.21 ml/min over 30 min. Then 30 min after stopping aminophylline, 150 mg/kg of etophylline (50 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min, followed by a maintenance dose of 30 mg/kg/hr in 27.6 ml at the rate of 0.23 ml/min over 2 hrs. 8

Treatment 4: 150 mg/kg of etophylline (50 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min. Then 30 min after stopping etophylline, 40 mg/kg of aminophylline in 6.3 ml D-5-W was administered by intravenous infusion at the rate of 0.21 ml/min over 30 min.

Blood samples were collected and centrifuged at 2000 rpm at 4°C for 30min.15 Plasma was separated and frozen until assayed.

Assay

25 pl of plasma was mixed with 25 pl of internal standard (120 lig/m1 of 8-hydroxypropyltheophylline16 in acetonitrile17 and centrifuged at 2000 rpm at 4°C for 30 min. The supernatant solution was separated from the depo- sited plasma protein and 10 pl injected into the HPLC system. Standard solutions were prepared in the same way as unknown samples, but using standard stock solutions to add to plasma to obtain 5, 10, 20, 30, 40, 50, 75, 90 and

100 pg/m1of etophylline or theophylline as well as a mixture of both. HPLC analyses were performed on a Water Associates

Chromatography pump, a model 440 absorbance detector, WISP

710B, a reverse phase p- Bondapak C18 column and a pre- column (10 cm long packed with C18 packingpowder).18 An Acetonitrile-water (7% V/V) mixture with acetic acid19 9

(pH = 6.0) was used as mobile phase at a flow rate of 2.0 ml/min. Absorbance was monitored at 280 nm. Peak height ratios were used for drug quantification.

Data were analyzed by AUTOAN2,2° and NONLIN21 programs.

The best fitted models by AUTOAN2 were chosen except for etophylline when administering etophylline in the presence of aminophylline. Terminal slopes of the post infusion data were fitted to a one compartment open model. Estimates obtained from AUTOAN2 or NONLIN were used to calculate pharmacokineticparameters.22 10

RESULTS AND DISCUSSION

Plasma theophylline concentration time curves for 6 rabbits each after administration of aminophylline alone, aminophylline followed by etophylline or etophylline followed by aminophylline are shown in Figures I.1, I.2a and I.3b, respectively. Data curves are essentially superimposable for all three figures. Typical individual plasma concentration time curves after the same treatments are shown in Figures 1.4-1.6. Each curve for theophylline is quite linear post infusion and distribution. All plasma theophylline concentration time curves were well described mathematically by assuming a two compartment open pharmacokinetic model with a rapid a distribution phase.

Pharmacokinetic parameters for theophylline are shown in

Tables I.1, I.2a and I.3c. All calculated pharmacokinetic parameters have been corrected for the infusion time (11).

Pharmacokinetic parameters after administering aminophylline alone (Table I.1, Figure I.1) show a mean elimination half-life of 5.2 hrs and mean Vd of 0.706 L/kg. These are consistent with data reported earlierfor rabbits by A.

El-Yazigi and R. J. Sawchuk (12) with mean elimination half-lives of 4.4 hrs and Vd of 0.708 L/kg. P. K. Ng and

R. A. Locock (13) also reported a mean elimination half- life of 5.5 hrs and Vd 0.545 L/kg. 11

1000.00

C.0 100.00 C)

10.00

.00 CO 4.00 x.00 00 CO 00 14.00 HOURS

Figure 1.1 Plasma concentration time curves for theophylline after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits. 12

1000.00

.00 1.00 4.00 g.00 fkoo =too td.00 14.00 HOURS

Figure I.2a Plasma concentration time curves for theophylline after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 13

1000.00

X 100.00 0C, X

0 X C .0.00

.00 00 .00 00 = 00 100 1 -CC HOURS

Figure I.2bPlasma concentration time curves for etophylline after administration of aminophylline (40 mg/kg intravenous infusionover 30 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusionover 2 hours) in 6 rabbits. 14

.00 Loa 4.00 Loo ri.00 icLoo d..00 ikoo HOURS

Figure I.3a Plasma concentration time curves for etophylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits. 15

100G-00

0 Z0 0

Ui C 10.00

C..

.00 Lao 4.00 6.00 ELoo loioo 14.00 HOURS

Figure I.3b Plasma concentration time curves for theophylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits. 16

1000.00

IJ 104.00 X

10.00

.00 £00 4.00 Lao Loo :oloo ld.00 :4.00 HOURS

Figure 1.4 Plasma concentration time curve for theophylline fitted by a two compartment open model after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) in subject D. 17

4.000.00

0 100.00 X N.#

10.00

.00 00 .00 00 = 00 1' 00 100 1 .00 HOURS

Figure 1.5 Plasma concentration time curve for theophylline (a) and etophylline (*) after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in subject Q. 18

1000.00

I 2 100.00 I

10.00

HOURS

Figure 1.6 Plasma concentration time curves for theophylline () fitted by a two compartment open model and etophylline (*) fitted by a three compartment open model after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in subject T. Table I.1Pharmacokinetic Parameters for Theophylline after Administering Aminophylline (40 mg/kg Intravenously over 30 min) in Rabbits

eta Rabbit Oa le Icel k12 k21 V1 Vd V2 a AUC Inventory code hr-I hr-1 hr hr-1 hr-I hr -1 L/kg 14/kg L/kg L/kiVLATIIIirml

BE 0.1365 0.3796 5.08 0.1719 0.0428 0.3014 0.4912 0.6186 0.1274 0.0844 400.9071

B 0.1160 0.6599 5.97 0.2052 0.1977 0.3731 0.6101 1.0794 0.4693 0.1252 273.6924

D 0.1833 3.5529 3.78 0.1995 0.2720 3.2647 0.5221 0.5683 0.0461 0.1041 300.0461

L 0.0967 5.4850 7.17 0.1046 0.4086 5.0684 0.8704 0.9420 0.0715 0.0911 366-3243

WW 0.1274 9.9999 5.44 0.1281 0.0523 9.9469 0.7059 0.7094 0.0038 0.0904 345.8782

A 0.1433 0.1634 4.84 0.1572 0.0005 0.1490 0.2898 0.3178 0.0281 0.0456 843.5346

Meant 0.1339 3.3735 5.18* 0.1611 0.1623 3.1839 0.5816 0.7059 0.1244 0.0901 421.7305

SDd 0.0293 3.8738 0.0396 0.1591 3.8656 0.1983 0.2729 0.1742 0.0262 211.6120

%CVe 21.88 114.83 24.58 98.03 121.41 34.09 38.66 140.02 29.12 50.18

Range 0.0967- 0.1634- 3.78- 0.1046- 0.0005- 0.1490-0.2898-0.3178- 0.0038-0.0456- 273.6924-

0.1833 9.9999 7.17 0.2052 0.4086 9.9469 0.8704 1.0794 0.4693 0.1252 843.5346

a from WNLIN program b 0.693/S c EX/N d (E(xi - M)2/(N - 1))/ e (S.D./Mean) x 100 * 0.693 /BMean Table I.2aPharmacokinetic Parameters for Theophylline after Administering Aminophylline (40 mg/kg Intravenously over 30 min) Followed by Etophylline (150 mg/kg Intravenously over 5 min and 30 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

(la Rabbit oa tit) kel k12 k21 VI Vd V2 CI AUC Inventory code hr-1 hr-I hr hr -1 hr -1 hr -1 L/kg Lkg L/kg L/kg/hr pg-hr/m1

A 0.1355 0.4918 5.11 0.1729 0.0690 0.3854 0.6144 0.7839 0.1695 0.1062 315.3580

DV 0.2290 0.3306 3.03 0.2451 0.0056 0.3088 0.4357 0.4663 0.0307 0.1068 507.0337

Q 0.0428 0.2201 16.19 0.0666 0.0549 0.1414 0.3697 0.5755 0.2059 0.0246 1327.4020

R 0.1236 0.3085 5.61 0.1788 0.0400 0.2133 0.3349 0.4843 0.1494 0.0598 529.0501

UU 0.1317 0.4987 5.26 0.1355 0.0101 0.4848 0.7193 0.7398 0.0205 0.0975 335.1944

F 0.1960 2.2200 3.54 0.2564 0.4627 1.6969 0.2434 0.2850 0.0415 0.0624 565.1265

Meant 0.1431 0.3450 4.84* 0.1759 0.1071 0.5384 0.4529 0.5558 0.1029 0.0762 596.5275

SIDO 0.0645 0.1249 0.0705 0.1760 0.5804 0.1800 0.1859 0.0812 0.0329 372.8477

%CVe 45.07 36.20 40.08 164.33 107.80 39.74 33.44 78.91 43.17 62.50

Range 0.0428- 0.2200- 3.03-0.0666- 0.0056- 0.1414-0.2434- 0.2850-0.0205-0.0267- 315.3584-

0.2290 0.4987 16.19 0.2564 0.4627 1.6969 0.7193 0.7839 0.2059 0.1160 1327.4020

a from NDNLIN program b 0.693/B c EX/N d IE(xi 3)2/(N e (S.D./Mean) x 100 * 0.693/0ftaan O Table I.2bPharmaookinetic Parameters for Etophylline after Administering Aminophylline (40 mg/kg Intravenous Infusion over 30 min) followed by Etophylline (150 mg/kg loading dose Intravenously over 5 min and 30 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hr) in Rabbits

Rabbit oa tib Inventory code hr-1 hr

A 0.2949 2.35

BV 0.1926 3.60

Q 0.2318 2.99

R 0.3238 2.14

UU 0.3815 1.82

F 0.5902 1.17

Meant 0.3161 2.19*

SOO 0.1175

KVe 37.17

Range 0.1926- 1.17-

0.5902 3.60

afrom MALIN program b 0.693/0 c EX/N d (Elxi Y)2/(N 1)1/ e (S.D./Mean) x 100 * 0.693/0 Mean Table I.3aPharmacokinetic Parameters for Etophylline Following Two Compartment Open Model After Administering Etophylline (150 mg/kg Intravenouslyover 5 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

ca Rabbit Oa tib kela k12a k2la Vla Vd V2 CI AUC Inventory code hr -1 hr -1 hr hr -1 hr -1 hr -1 L/kg L/kg L/kg L/kg/hr Vg-hr /m1

S 0.3165 7.522 2.19 0.89 4.28 2.67 0.6190 1.2062 0.5872 1.3248 392.91

DD 0.3795 12.243 1.83 0.97 6.88 4.77 0.3912 1.1176 0.7264 0.3794 294.48

CC 0.3604 6.651 1.92 1.07 5.97 3.59 0.2835 1.4215 1.1380 0.3034 309.59

Meant 0.3521 8.80531.97* 0.98 5.71 3.68 0.4312 1.2484 0.8172 0.6692 332.33

SDd 0.0323 3.0088 0.09 1.32 1.05 0.1713 0.1563 0.2864 0.5690 53.01

liCVe 9.17 34.17 9.21 23.11 28.61 39.73 12.52 35.05 85.03 15.95

Range 0.3165- 6.651-1.83- 0.89- 4.28- 2.67- 0.2835- 1.1176- 0.5872- 0.3034-294.48-

0.3795 12.243 2.19 1.07 6.88 4.77 0.6190 1.4215 1.1380 1.3248 392.91

a from AU AN 2 b 0.693/0 c EX/N d lE(xi 302/(N 1)11 e (S.D./Mean) x 100 * 0.693 /S Mean Table I.3bPharmacokinetic Parameters for Etophylline Following ThreeCompartment Open Model Behavior After Administering Etophylline (150 mg/kg Intravenouslyover 5 min) Followed by Aninophylline (40 mg/kg Intravenous Infusionover 30 min) in Rabbits

a a Rabbit Oa Y tib kel V1 Vd Cl AUC Inventory code hr-1 hr-1 hr-1 hr hr-1 L/kg L/kg L/kg/hrpg-hr/m1

JJ 0.1466 0.6180 14.188 4.73 0.9250 0.2338 1.4752 0.2163 495.0076

MM 0.2706 1.3158 15.588 2.56 0.9456 0.4840 1.6914 0.4577 334.0987

T 0.2706 1.3156 15.588 2.56 0.9456 0.3455 1.2075 0.3267 334.1114

Meanc 0.2293 1.0831 15.12173.02* 0.9387 0.3544 1.4580 0.3336 387.7392

SDd 0.0716 0.4028 0.8082 0.0119 0.1253 0.2424 0.1208 92.8971

%CVe 31.22 31.19 5.351 1.27 35.37 16.63 36.22 23.96

Range 0.1466- 0.6180-14.188-2.56- 0.9250- 0.2338- 1.2075- 0.2163-334.0987-

0.2706 1.3158 15.5884.73 0.9456 0.4840 1.6914 0.4577 495.0076

afrom AUTOAN 2 b 0.693/e. c EX/N d [E(ki - 2)2/(N 1)]/ e (S.D./Mean) x 100 * 0.693/f3Man Table I.3c Pharmacokinetic Parameters for Theophylline after Administering Etophylline (150 mg/kg Intravenously over 5 min) Followed by Aminophylline (40 mg/kg intravenous Infusion over 30 min) in Rabbits

0a tit) Rabbit 8a kel k12 k21 V1 Vd V2 Cl AUC Inventory code hr-1 hr-1 hr hr-1 hr -1 hr-1 L/kg L/kg L/kg 14/kg/hr pg-hr/m1

CC 0.1084 0.1346 6.39 0.1132 0.0009 0.1289 0.6063 0.6329 0.0266 0.0686 235.5704

DD 0.0938 4.8884 7.39 0.1008 0.3335 4.5478 0.6158 0.6619 0.0461 0.0621 525.5433

JJ 0.1154 6.6679 6.01 0.1232 0.4131 6.2470 0.6333 0.6759 0.0426 0.0780 392.2411

MN 0.0824 3.1512 8.41 0.1075 0.7106 2.4155 0.6057 0.7903 0.1845 0.0651 495.1086

S 0.1353 1.6770 5.12 0.1496 0.1456 1.5171 0.6568 0.7261 0.0692 0.0982 322.0334

T 0.1833 3.1472 3.78 0.2005 0.2524 2.8776 0.6746 0.7378 0.0632 0.1353 244.2894

Meanc 0.1198 3.2777 5.78* 0.1325 0.3094 2.9557 0.6321 0.7042 0.0720 0.0846 369'1310

SO 0.0360 2.3049 0.0374 0.2439 2.1783 0.0284 0.0578 0.0572 0.0281 123.7023

%CVe 30.05 70.32 28.23 78.83 73.70 4.50 8.21 79.39 33.19 33.51

Range 0.0824- 0.1346- 3.78- 0.1008- 0.0009-0.1289- 0.6057-0.6329-0.0266- 0.0621-235.5704-

0.1833 6.6679 8.41 0.2005 0.7106 6.2470 0.6746 0.7903 0.1845 0.1353 525.5433

afrom NONLIN program b 0.693/8 c EX/N dfE(xi - 3)2/(N 1)11 e (S.D./Mean) x 100 * 0.693/8 Mean 25

The a elimination phase was quite variable in all three treatments (Tables I.1, I.2a and I.3c). Analysis of variance and Kruskal-Wallis test showed that differences in

S elimination rate constants, Vd (Volume ofdistribution) and area under the curve (AUC), among the treatments are not significant (P < 0.05). In one case where one subject (rabbit A) received two treatments, a was essentially the same when the rabbit receivedaminophylline followed by etophylline (Table I.2a - 0.136hr-1), compared to when aminophylline was given alone (Table I.1 - 0.143hr-1). Theophyllines' elimination half-life differed by only about

5.5% (5.1 hr vs. 4.8 hr). However, in this one rabbit the total volume of distribution, Vd was about 2.5 timeslarger

for theophylline given alone (0.7839 L/kg versus 0.3178

L/kg). In man, theophylline is mostly eliminated bybiotrans-

formation in the liver followed by urinary excretion ofits

metabolites. Approximately 7-13% is excreted unchanged in

the urine. About 53 to 65% of theophylline is reversibly

bound to plasma protein (14). Etophylline, in man, is also mainly eliminated by biotransformation and about 20% is

excreted unchanged in the urine (6). There is no infor-

mation available on etophylline protein binding. Small

changes in theophylline protein binding areinsignificant

as far as theophylline distribution,metabolism and excre-

tion are concerned (15). Since average changes are small 26 and overall there is no statistical difference in Vd or 8, one must conclude that etophylline has no significant effect on the pharmacokinetic behavior of theophylline, including protein or tissue binding, when administering etophylline concomitantly with aminophylline.

Plasma etophylline concentration time curves for 6 rabbits each after administration of etophylline alone, etophylline followed by aminophylline, or aminophylline followed by etophylline are shown in Figures 1.7, I.3a and

I.2b. Data in Figures 7 and 3a are superimposable. Typical etophylline plasma concentration time curves for all the treatments administered are shown in Figures 1.5,

1.6, 1.8 and 1.9. Data for etophylline administered alone were well described by a two compartment open model for 3 rabbits and a three compartment open model for the other 3 rabbits, as determined by AUTOAN2. Pharmacokinetic parameters are shown in Tables I.4a and I.4b. Differences in 8, ti, Vd and AUC are not statistically significant for the groups of rabbits best described by the two vs. three compartment open models. Overall average ti was 1.7 hr. Pharmacokinetic parameters for bolus etophylline when followed by aminophylline infusion were also obtained from either a two compartment open model or a three compartment open model as determined by AUTOAN2, depending on the subject as shown in Tables I.3a and I.3b. There is also no statistically significant difference in 8, Vd or AUC bet- 27

1000.00

100.00

10.00

.00 00 .00 00 00 100 00 1 .00 HOURS

Figure 1.7 Plasma concentration time curve for etophylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) in 6 rabbits. 28

100040

.100'.00

10.00

.00 00 0.00 = 00 tr 1..00 1 .0;, HOURS

Figure 1.8 Etophylline plasma concentration time curve fitted by a two compartment open model after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) in subject S. 29

1000.00

100.00 I(.9 a O

Q 10.00

.00 00 .00 0.00 = 00 1 00 1 .00 1 .00 HOURS

Figure 1.9 Etophylline plasma concentration time curve fitted by a three compartment open model after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) in subject EE. Table I.4aPharmacokinetic Parameters for Etophylline Following TWo Obmpartment Open Model After Administering Etophylline (150 mg/kg Intravenously over 5 min) in Rabbits.

t }b Cl AOC Rabbit fla a4 kela k12a k21a Vla Vd V2 Inventory code hr -1 hr-1 hr hr -1 hr -1 hr -1 14/kg 14/kg b/kg 14/kg/hrughr/mi

PS 0.3198 5.8831 2.17 2.14 2.90 1.02 0.1086 0.8578 0.7492 0.2324 438.53

S 0.5092 5.3480 1.36 2.32 1.42 0.90 0.2039 1.4763 1.2724 0.4730 236.78

XX 0.4059 2.9309 1.71 1.03 0.69 1.21 0.3819 1.0825 0.7006 0.3934 229.72

Meant 0.4116 4.7207 1.68* 1.83 1.67 1.04 0.2315 1.1389 0.9074 0.3663 301.68

SO 0.0948 1.5729 0.70 1.13 0.16 0.1387 0.3131 0.3170 0.1226 118.57 33.46 39.30 %CVe 23.04 33.32 38.18 67.43 15.03 59.92 27.49 34.94

229.72- Range 0.3198- 2.9309- 1.36- 1.03- 0.69- 0.90- 0.1086- 0.8578-0.7006- 0.2324-

0.5092 5.8831 2.17 2.32 2.90 1.21 0.3819 1.4763 1.2724 0.4730 438.53

afrom ADMAN 2 b 0.693/0 c EX/N d D2(xi - -1)2/(N - 1)1/ e (S.D./Mean) x 100 * 0.69343 Mean Table I.4bPharmacokinetic Parameters for Etophylline Following Three COmpartment Open Model Behavior After Administering Etophylline (150 mg/kg Intravenously over 5 min) in Rabbits

Rabbit fla aa /a ti D kel V1 Vd Cl AUC Inventory code hr -1 hr -1 hr -1 hr hr -1 L/kg L/kg L/kg/hrug-hr/m1

U 0.5381 2.624 27.603 1.29 3.9414 0.1214 0.8892 0.4785 319.32

T 0.3151 0.911 17.726 2.20 1.2758 0.2611 1.0573 0.3332 358.01

a; 0.3055 1.497 14.628 2.27 1.1490 0.3071 1.1549 0.3528 432.94

Meant 0.3862 1.6773 19.98571.79* 2.1221 0.2299 1.0338 0.3882 37009

SDd 0.1316 0.8706 6.7762 1.5769 0.0967 0.1344 0.0788 5777

%CVe 34.08 51.91 33.91 74.31 42.07 13.00 20.31 15.61

Range 0.3055- 0.911- 14.628-1.29- 1.1490- 0.1214- 0.8892- 0.3332- 31932-

0.5381 2.624 27.603 2.27 3.9414 0.3071 1.1549 0.4785 432'94

a from AUTOAN 2 b 0.693A c EX/N d (E(xi X)2 /(N e (S.D./Mean) x 100 * 0.693 /S Mean 32 ween these groups of subjects best described by the two vs. three compartment models. Etophylline 13and ti when administering aminophylline followed by both a loading dose and maintenance dose of etophylline are shown in Table I.2b

(Figures I.2b and 1.5). The (3elimination values for etophylline were determined by regression of postinfusion data. Etophylline plasma concentration time curves are shown in Figure I.2b. Only 2 of 6 rabbits reached steady state when all received the same loading dose (150 mg/kg) and maintenance dose (30 mg/kg/hr for 2 hr). This indica- tes a high variation in elimination rate which was also reported in humans (6). Overall, analysis of variance and Kruskal-Wallis test showed that differences in ti among treatments are not significant. However, for two individual rabbits that received two treatments with etophylline, the half-life was longer when etophylline followed by aminophylline was administered vs. etophylline administered alone. This effect occured for both subject T (2.6 vs 2.2 hr) which was described by a triexponential equation (Tables I.3b and I.4b) and subject

S (2.2 vs 1.4 hr), described by a biexponential equation

(Tables I.3a and I.4a). This effect may be caused by com- petition for the same enzyme in a metabolic pathway. Overall grouped animal data show no differences in a, .4,

Vd or AUC. Therefore, on the average, theophylline had no effect on etophylline pharmacokinetic behavior when admi- 33 nistered concomitantly with etophylline. For the two indi- viduals which received cross-over treatments, theophylline increased etophyllines' ti by 18 to 50 percent which may be a real effect but is most likely only a result of intrasub- ject variation.

Rabbits became "jumpy" and exhibited some minor muscular fasciculations at plasma theophylline concentrations of about 100 mcg/ml. Death preceeded by a generalized con- vulsion occurs at about 250 to 400 mcg/ml as observed in our laboratory. No side effects were observed for etophylline even at plasma concentrations as high as 700 mcg/ml. It is remarkable that no drug toxicities were observed with concomitant aminophylline (theophylline plasma concentrations of 50-100 mcg/ml) and etophylline bolus injection plus infusion (Figure I.2b) plasma concentrations maintained for two hours at 100 to 300 mcg/ml.

Total plasma methyl xanthine concentrations were up to 400 mcg/ml without apparent additive or synergistic toxicities. 34

CONCLUSION

Etophylline and theophylline pharmacokinetics in rabbits when administered concomitantly do not differ from

those when administered alone. There were no apparent additive toxicities in the doses studied. These results

suggest that etophylline and theophylline could be admi-

nistered concomitantly without complication. However, further study with larger populations and in humans are

necessary before it can be concluded that concomitantadmi-

nistration of the drugs is clinically safe. 35

ENDNOTES

1. Sterile Alcohol Prep. Professional Disparables, Inc. Mt. Vernon, N.Y. 10500-1890, Missisangna, Ontario L4T

1GE, Canada.

2. Lidocaine Hydrochloride injection USP 2% (2 mg/ml)

Rugby Laboratories, Inc. Rockville Center, L.I., N.Y.

3. Quik -Cath® Travenol Laboratories, Inc. Deerfield, IL.

4. Intermittant infusion plug. Argyle, St. Louis, MO.

5. 8-Hydroxyethyltheophylline. Sigma Chemical Company.

St. Louis, MO.

6. Dextrose 5% in water. Abbott Laboratories, North

Chicago, IL.

7. Acrodisc ®. Disposable Filter Assembly. Gelman.

8. Aminophylline injection USP 250 mg (25 mg/ml). Abbott Laboratories, North Chicago, IL.

9. Infusion/Withdrawal Pump, model 902. Harvard Apparatus

Co. Inc., Millis., Mass.

10. Life Care® IV Pump. Abbott Laboratories, North

Chicago, IL.

11. Hypodermic needle sterile. Becton Dickinson and Company, Rutherford, NJ.

12. Intramedic® Polyethylene tubing PE90.

13. Microcentrifuge tube. Centaur Sciences, Inc., 36

Standford, CT.

14. Panheprin ®, Heparin sodium injection USP., Abbott

Laboratories, North Chicago, IL.

15. Model TJ-6 Centrifuge, Model TJ-R Refrigeration Unit.

Beckman Instruments, Palo Alto, CA.

16. 8-Hydroxypropyltheophylline. Sigma Chemical Company,

St. Louis, MO.

17. Acetonitrile, HPLC. J.T. Baker Chemical Co.,

Phillipsburg, NJ.

18. Waters Associates, Inc. Milford, MA.

19. Acetic acid. J.T. Baker Chemical Co., Phillipsburg,

NJ. 20. A.J. Sedman and J.B. Wagner, "AUTOAN is a Decision Making Pharmacokinetic Digital Computer Program," Publication Distribution Service, Ann Arbor, MI., 1976.

21. C.M. Metzler, G.L. Elfring and A.J. McEwen, "A Users Manual for NONLIN and Associated Programs," The Upjohn

Co., Kalamazoo, MI., 1974.

22. M. Gibaldi and D. Perrier, "Pharmacokinetics," Dekker,

New York, NY., 1975 37

REFERENCES

1. J. Zuidema and F. W. H. M. Merkus, "Clinical and

Biopharmaceutical Aspects of Theophylline and its

Derivatives", Curr. Med. Res. Opin., 6, suppl. 6, 14

(1979).

2. P. A. Mitenko and R. I. Ogilvie, Clin. Pharmac.

Therp., 16, 720 (1974).

3. "Physician's Desk Reference," Ed., Medical Economics Company, Oradell N.J., 1982, pp. 1754.

4. "Martindale, The Extra Pharmacopoeia," N. W. Blacow, Ed., 27th ed., Pharmaceutical Press, London, England,

1977, p. 279.

5. J. G. R. Ufkes, R. S. Leeuwin, M. Ottenhof, A. Zeegers and J. Zuidema, "Efficacy of Theophylline and its N-7-subsituted Derivatives in Experimentally Induced

Bronchial Asthma in the Guinea-Pig," Arch. Int.

Pharmacodyn., 253, 301 (1981).

6. J. Zuidema, J. Verhoeven and F. W. H. M. Merkus, "Pharmacokinetics of Etophylline after Intravenous and

Oral Administration to Humans," Int. J. Clin.

Pharmacol., Vol. 19, No. 7, 310 (1981).

7. R. Jauch, and A. Zimmer, "Human Pharmacokinetic von

Oxyathyltheophyllin and Fominoben HC1," Arzneim. 38

Forsch., 28, 693 (1978).

8. P. L. Sharma and R. M. Sharma, "Comparative Bioavailability of Sustained-Release and Conventional Tablets of Hydroxyethyltheophylline in man," Int. J.

Clin. Pharmacol., Vol. 17, No. 9, 394 (1979).

9. P. A. Mitenko and R. I. Ogilvie, "Rational Intravenous

Doses of Theophylline," N. Engl. J. Med., 289,

600(1973).

10. J. Zuidema and F. W. H. M. Merkus, "Pharmacokinetics and Pharmacodynamics of Diprophylline," Pharm.

Weekbl., Sci. Ed., Vol. 3, No.5, 1320(1981).

11. J. C. K. Loo and S. Riegelman, "Assessment of Pharmacokinetic Constants for Postinfusion Blood

Curves Obtained After I.V. Infusion," J. Pharm. Sci.,

Vol 59, No. 1, 53(1970).

12. A. El-Yazigi and R. J. Sawchuk, "Theophylline Absorption and Disposition in Rabbits: Oral,

Intravenous, and Concentration-Dependent Kinetic

Studies," J. Pharm. Sci., Vol. 70, No.4 (1981).

13. P. K. Ng and R. A. Locock, "Comparative Pharmacokinetics of Theophylline and Dyphylline Following Intravenous Injection in Rabbits," Research

Communications in Chemical Pathology and Pharmacology,

Vol. 26, No.3 (1979).

14. R. I. Ogilvie, "Clinical Pharmacokinetics of Theophylline," Clin. Pharm. 3: 267 (1978). 39

15. "Evaluation of Drug Interactions," 2nd Ed., The

American Pharmaceutical Association, Washington DC.,

1976, p. 321. 40

CHAPTER II

PROXYPHYLLINE AND THEOPHYLLINE PHARMACOKINETICS WHEN ADMINISTERED

CONCOMITANTLY 41

ABSTRACT

Proxyphylline and theophylline were given alone and concomitantly to rabbits. Theophylline plasma concentration time curves were well described by either a one compartment open model for some subjects or a two compartment open pharmacokinetic model for others with mean half- lives of 3.89 and 5.46 hr when admininstering aminophylline followed by proxyphylline. Mean Vd was 0.62 and 0.82 L/kg respectively when aminophylline was administered following proxyphylline the mean theophylline half-lives were 4.47 and 4.42 hr with Vd of 0.39 and 0.78 L/kg for one and two compartment open models respectively. Plasma concentration data for bolus proxyphylline were fitted by either a two or three compartment open model with mean half-lives of 2.85 and 4.61 hr and meanVd of 0.98 and 1.49 L/kg respectively and mean half-lives of 3.86 (two compartment) and 5.63 hr (three compartment) with Vd of

1.15 (two compartment) and 1.66 L/kg (three compartment) when followed by aminophylline. Proxyphylline given as a bolus loading dose with an infusion maintenance dose in the presence of aminophylline had a meanhalf-life of 3.41 hr. Overall analysis of variance and Kruskal-Wallis test showed that differences among $ and Vd for proxyphylline or 42 for theophylline in the different treatments were not statistically significant at a= 0.05. 43

INTRODUCTION

Proxyphylline is an N-7 substituted theophylline derivative, a-hydroxypropyltheophylline which was introduced in

1956 (1). Proxyphylline is an effective bronchospasmolytic agent (2). It has been used outside the United States in the treatment of asthma and obstructive lung disease (3). Proxyphylline products are available commercially in many different pharmaceutical preparations such as injectable solution, tablets, slow-release tablets and suppositories. The preparations contain both proxyphylline alone and in combination with other xanthines such as dyphylline or dyphylline and theophylline (4-5). Proxyphylline was postulated to have lower side effects than theophylline (6) and be better tolerated orally and by injection (Martindale pp. 348). Proxyphylline plasma concentrations of above 90 pg/ml were reported with no severe side effects and no adverse cardiovascular reaction or skeletal muscular tremor when given intravenously (7). In one case when the proxyphylline plasma concentration was as high as 180 pg/ml in a female, no severe side effects were observed (8). Proxyphylline plasma concentrations that cause bronchodilation were reported as 13 pg/ml but correlation 44 between proxyphylline plasma concentration and bronchodila-

tion was not observed (6). The potency of proxyphylline was reported to be 0.2 and 0.6 times that of theophylline

in relaxing the guinea pig trachea (2,9). In humans, proxyphylline was reported to be 5 and 7 times less potent

than theophylline (10,1). Proxyphylline at concentrations

of about 18 ilg/m1 produces clinically noticeable reversion

of airway obstruction (11). Proxyphylline is excreted 21-29% unchanged in the

urine and the rest is metabolized. Therefore, proxyphylline is mainly eliminated by biotransformation with both proxyphylline and its metabolites being excreted

in urine. Theophylline was not one of its metabolites

(12). Proxyphylline has its own pharmacokinetics and phar-

macodynamics. Proxyphylline pharmacokinetics in man were studied and half-lives were reported to be 3, 4.3, 6.5 and

8 hrs. The volume of distribution was reported to be

about 0.6 L/kg. Because of undesirable properties of theophylline as stated in Chapter I, proxyphylline may be more useful than theophylline and theophylline salts in emergency cases in

countries where proxyphylline is used. Proxyphylline could replace aminophylline for intravenous administration if it

is safe and effective when given as an intravenous bolus to

patients who have been taking theophylline preparations.

This study was undertaken to investigate the pharmaco- 45 kinetic behavior and gross toxicity of theophylline and proxyphylline when given alone and concomitantly in rabbits. 46

MATERIALS AND METHODS

Female New Zealand white rabbits weighing 1.9-3.45 kg were used in this study. Six rabbits each were used in each treatment except for treatment 2, where seven rabbits were used. The materials and methods used in preparation of proxyphylline) solution for injection, preparation of the rabbits, blood sample collection and sample storage were the same as described in materials and methods in

Chapter I.

Drug Administration Treatments

Treatment 1: Same as Treatment 1 in Chapter I

Treatment 2: 135 mg/kg of proxyphylline (100 mg/ml) was administered by intravenous infusion at the rate of

1.02 ml/min over 3-5 min.

Treatment 3: 40 mg/kg of aminophylline2 in 6.3 ml of solution was administered by intravenous infusion at the rate of 0.21 mg/min over 30 min. Then 30 min after stopping aminophylline, 135 mg/kg of proxyphylline (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min, followed by a maintenance dose of 15 mg/kg/hr of proxyphylline which was administered at the rate of of 0.23 ml/min over 2 hrs.

Treatment 4: 135 mg/kg of proxyphylline (100 mg/ml) 47 was administered by intravenous infusion at the rate of

1.02 ml/min over 3-5 min. Then 30 mins after stopping proxyphylline, 40 mg/kg of aminophylline in 6.3 ml solution was administered by intravenous infusion at the rate of

0.21 ml/min over 30 mins.

Assay Plasma samples were collected, stored and analysed by

the same methods as described in Chapter I. The internal

standard used was 8-hydroxyethyltheophylline.3 Data were

also analysed by the same procedures as in Chapter I. 48

RESULTS AND DISCUSSION

Theophylline plasma concentration vs. time curves for

6 rabbits each after administration of aminophylline alone are shown in Chapter I, Figure I.1. A typical theophylline plasma concentration time curve is shown in Figure 1.4.

Plasma concentration of theophylline vs. time curves for 6 rabbits each after administration of aminophylline followed by proxyphylline or proxyphylline followed by aminophylline are shown in Figures II.la and II.2b respectively. Typical individual plasma concentration time curves after the same treatments are shown in Figures 11.3 and 11.4. Theophylline pharmacokinetic parameters after administration of aminophylline followed by proxyphylline loading dose and maintenance dose are shown in Table II.la and II.lb. All pharmacokinetic parameters havebeen corrected for infusion time (13). Five of six rabbits were best described (Table II.lb) by a two compartment open model with a mean ti of 5.5 hr and mean Vd of 0.82 L/kg.

The other rabbit (BA) was best described by a one compartment open model (Table II.la) as determined by AUTOAN2. Subject BA had a half-life of 3.89 hr and a Vd of 0.62

L/kg. Theophylline pharmacokinetic parameters after administration of proxyphylline followed by aminophylline 49

1000.00

x3 100.00 x

0 C) I U) 10.00 0J

.00 .00 4.00 6.00 Lou 101.00 1100 14.00 HOURS

Figure II.la Plasma concentration time curves for theophylline after the administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 50

1000.00

X CD 100.00

10.00

.00 .00 .00 -.00 HOURS

Figure II. lb Plasma concentration time curves for proxyphylline after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) and proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 51

1000.00

0 0z 0

4CL

.00 .00 4.00 .00 4.00 10! oo 1Z.00 a .00 HOURS

Figure II.2a Plasma concentration time curves for proxyphylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in 6 rabbits. 52

1000.00

3 M -.. 100.00 0 M ,.... C) 0Z C) I.Q LO JC 10.00

.00 .00 .00 00 1 .00 1 00 HOURS

Figure II.2b Plasma concentration time curves for theophylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes) in 6 rabbits. 53

1000.00 7

x 100.00 C.>

0 O ICZ Ul ott 10.00 7 a.

.00 x.00 .00 6.00 .00 10.00 1i00 lkoo HOURS

Figure II. 3 Plasma concentration time curve for theophylline (0) and proxyphylline (:N.,) after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15mg/ kg/hr over 2 hours) in subject BE. 54

1000.00

I 0 100.00 I

.00 .00 00 .00 -.00 .00 1 00 HOURS

Figure 11.4 Typical plasma concentration time curves for tneophylline0 and proxyphylline (0) after the administration of proxyphylline(135 mg/kg intravenous infusion over 5 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes)in subject HH. Table II.laPharmacokinetic Parameters for Theophylline Following One Compartment Open Model Behavior After Administering Aminophylline (40 mg/kg Intravenous Infusion over 30 min) Followed by Proxyphylline (135 mg/kg Loading Dose Intravenous Infusion over 5 min and 15 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hr) in Rabbits

Rabbit kela till Vda Cl AUC Inventory code hr-1 hr L/kg L/kg/hr pg-hr/m1

BA 0.1782 3.89 0.6180 0.1101 912.21

a from AUTOAN2 b0.693/kel Table II.lbPharmacokinetic Parameters for Theophylline Following Two Compartment Open Model Behavior After Administering Aminophylline (40 mg/kg Intravenous Infusion over 30min) Followed by Proxyphylline (135 mg/kg Loading Dose Intravenously over 5 min and 15mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Ba tyb Rabbit as kela k12a k21a Vla Vc1 V2 CI AUC Inventory code hr-1 hr-1 hr hr -1 hr 1 hr -1 L/kg L/kg L/kg L/kg/hr aghr/m1

W 0.1328 24.6900 5.22 0.57 18.50 5.76 0.1768 0.7297 0.5529 0.0969 347.81

BE 0.0805 8.4132 8.61 0.31 5.99 2.20 0.1859 0.7186 0.5327 0.0578 561.84

G 0.1576 2.5937 4.40 0.25 0.85 1.66 0.4695 0.6961 0.2266 0.1097 292.63

0.1201 2.7599 5.77 0.21 1.10 1.57 0.4677 0.7907 0.3230 0.0950 336.74

B 0.1439 9.1755 4.82 0.46 5.98 2.88 0.3379 1.1415 0.8036 0.1643 214.59

Meant 0.1270 9.5265 5.46* 0.36 6.48 2.81 0.3276 0.8153 0.4878 0.1047 350.72

SDd 0.0294 9.0159 0.15 7.17 1.73 0.1438 0.1857 0.2244 0.0385 129.11

%CVe 23.15 94.64 41.67 110.65 61.57 43.89 22.78 46.00 36.77 36.81

Range 0.0805- 2.5937-4.40- 0.21- 0.85- 1.57- 0.1768- 0.6961- 0.2266-0.0578- 214.59-

0.1576 24.6900 8.61 0.57 18.50 5.76 0.4695 1.1415 0.8036 0.1643 561.84

a from AUTOANQ b 0.693/0 c EX/N d [E(xi - 102/04 - e (S.D./Mean) x 100 * 0.693 /0M an 57

(Figure II.2b) are shown in Tables II.2a and II.2b. Three rabbits each were best described by a one compartment open model or a two compartment open model with mean half-lives of 4.47 and 4.42 hr and Vd of 0.39 and 0.70 L/kg respectively. Theophylline pharmacokinetic parameters after administration of aminophylline alone are shown in Table I.1

(Chapter I). Data were well described by a two compartment open model with mean half-live of 5.18 hrand Vd of 0.71

L/kg. Thus, proxyphylline administration prior to aminophylline may have affected the Vd (average 45% decrease)

in the rabbits with two compartment behavior or changed theophylline distribution characteristics to induce three

compartment behavior in some rabbits (Tables II.2aand

II.2b vs. Table I.1). However, analysis of variance and Kruskal-Wallis test showed that differences inelimination rate constants, Vd (volume of distribution) and AUC(area

under the curve), among the treatments are notsignificant. Therefore, one must conclude that proxyphylline has no

significant effect on theophylline pharmacokineticbehavior

when administering proxyphylline concomitantlywith ami-

nophylline under the conditions studied herein. Proxyphylline plasma concentration time curves for 7

rabbits after administration of proxyphylline alone are

shown in Figure 11.5. Proxyphylline plasma concentration Table II.2aPharmaookinetic Parameters for Theophylline Following One Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenous over 5 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

Rabbit kela fib Vda Cl AUC Inventory code hr-1 hr L/kg L/kg/hr pghr/m1

HH 0.1860 3.73 0.4203 0.0782 521.41

J 0.1200 5.78 0.2473 0.02971075.77

SS 0.1587 4.37 0.5165 0.0820 620.27

Meanc 0.1549 4.47* 0.3944 0.0633 739.15

SDd 0.0332 0.1360 0.0292 295.68

%CVe 21.41 34.49 46.13 40.00

Range 0.1200- 3.73- 0.2473-0.0297- 521.41-

0.1860 5.78 0.5165 0.0820 1075.77

afrom AUTOAN2 b 0.693A c E X/N d [E(xi 3T)2/(N 1)0 01 e (S.D./Mean) x 100 * 0.693/R Mean Table II.2bPharmacookinetic Parameters for Theophylline Following TWo Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

Rabbit oa as tib kel k12a k21a Vie Vd V2 Cl AUC Inventory hr-1 hr code hr-1 hr -1 hr -1 hr -1 L/kg L/kg L/kg L/kg/hr ug-hr/m1

I 0.1922 2.0468 3.61 0.28 0.56 1.40 0.3708 0.5220 0.1512 0.1003 313.59

II 0.1814 16.1324 3.82 1.20 12.70 2.44 0.0680 0.4199 0.3519 0.0762 419.27

0.0968 2.0151 7.16 0.33 1.19 0.59 0.3535 1.1666 0.8131 0.1129 285.18

Meanc 0.1568 6.7314 4.42* 0.60 4.82 1.48 0.2641 0.7028 0.4387 0.0965 339.35

SDd 0.0522 8.1415 0.52 6.83 0.93 0.1700 0.4049 0.3394 0.0186 70'66

%CVe 33.32 120.95 86.22 141.79 62.66 64.39 57.61 77.36 19.32 20.82

Range 0.0968- 2.0151- 3.61- 0.28- 0.56- 0.59- 0.0680-0.4199-0.1512- 0.0762- 285.18-

0.1922 16.1324 7.16 1.20 12.70 2.44 0.3708 1.1666 0.8131 0.1129 419.27

a from AUTOAN2 b 0.693/$ c EX/N d(E(xi - X)2/(N e (S.D./Mean) x 100 * 0.693/0Mean 60

1000.00

100.00

10.00

.00 oo too 4.00 &co itloo 14.o0 1.1.o0 HOURS

Figure 11.5 Plasma concentration time curves for proxyphylline after administration ofproxyphylline (135 mg/kg intravenous infusion over 5minutes) in 6 rabbits. 61

time curves for 6 rabbits each after administration of proxyphylline followed by aminophylline or aminophylline

followed by proxyphylline are shown in Figures II.lb and

II.2a. Typical proxyphylline plasma concentration time curves for all the treatments are shown in Figures 11.3,

11.4, and 11.6. Data for proxyphylline administered alone were well

described by a two compartment open model for 3 rabbits and

a three compartment open model for 4 rabbits asdetermined

by AUTOAN2, depending on the subjects as shown in Tables

II.3a and II.4b, with mean half-lives of 2.85 and 4.61 hr

and mean Vd of 0.98 and 1.49 L/kg respectively. Proxyphylline pharmacokinetic parameters when followed by aminophylline were also described by either a two compart-

ment open model or a three compartment open model with mean half-lives of 3.86 and 5.63 hr and mean Vd of 1.15 and 1.66

L/kg as shown in Tables II.3b and II.4a.

Proxyphylline8 and ti when administering aminophylline followed by a loading dose and maintenance dose

of proxyphylline are shown in Table 11.5. The 8 elimina-

tion values for proxyphylline were determined by regression

of post infusion data. Proxyphylline plasma concentration time curves are shown in Figure II.lb and 11.3. Data in Figures II.lb, II.2a and 11.5 are superimposable and very

similar to post infusion data, Table 11.5. Thus, concomitant theophylline did not influence the phar- 62

1000.00

100.00

10.00

.00 .00 .00 .00 .00 1 00 1 .00 1 .00 HOURS

Figure 11.6 Typical plasma concentration time curve for proxyphylline after administering proxyphylline (135 mg/kg by intravenous infusion over 5 min) in subject RR. Table II.3aPharmacokinetic Parameters for Proxyphylline Following Two Compartment ()pen MOdel Behavior After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) in Rabbits

Rabbit 0 a a 41) kela k12a k2la Via Vd V2 Cl AUC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 1,/kg 1kg Wkg t/kg/hr pg-hr/m1

P 0.2550 2.9591 2.72 0.66 2.65 2.16 0.5828 1.0931 0.5130 0.2787 496.68

FF 0.2837 13.7332 2.44 1.14 9.59 3.45 0.2591 0.8402 0.5811 0.2384 576.62

YY 0.1902 11.9200 3.64 0.45 6.87 4.62 0.5471 1.0108 0.4637 0.1923 725.67

Meant 0.2430 9.5374 2.85* 0.75 6.37 3.41 0.4630 0.9814 0.5184 0.2365 599.66

SO 0.0479 5.7686 0.35 3.50 1.23 0.1775 0.1290 0.0591 0.0432 116.22

%CVe 19.71 60.48 47.16 54.90 36.08 38.33 13.14 11.40 18.28 19.38

Range 0.1902- 2.9591- 2.44- 0.45- 2.65- 2.16- 0.2591- 0.8402-0.4637- 0.1923-496.68-

0.2837 13.7332 3.64 1.14 9.59 4.62 0.5828 1.0931 0.5811 0.2787 725.67

a from AUTOAN2 b 0.693/0 c EX/N d (E(xi - X)2 /(N 1)11 e (S.D. /Mean) x 100 * 0.693/$Mean Table II.3bPharmacokinetic Parameters for Proxyphylline Following Three Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenously over 5 min) in Rabbits

a Rabbit e la -Lib Vi Vd Cl AUC Inventory code hr-1 hr-1 hr-1 hr L/kg L/kg L/kg/hr lig-hr/m1

J 0.1541 0.880115.8278 4.50 0.2009 1.6567 0.2553 540.05

K 0.1311 0.2423 14.2646 5.29 0.2064 1.0645 0.13961992.67

CMG 0.0871 0.4441 17.9902 7.96 0.2308 2.1330 0.1858 736.17

RR 0.2293 1.152216.9099 3.02 0.2331 1.1094 0.2544 542.26

Meanc 0.1504 0.6797 16.2481 4.61* 0.2178 1.4909 0.2088 952.79

SDd 0.0595 0.4124 1.5899 0.0165 0.5057 0.0564 699.32

KVe 39.56 60.68 9.79 7.58 33.92 27.03 73.40

Range 0.0871- 0.2423-14.2646-3.02- 0.2009- 1.0645- 0.1396- 540.05-

0.2293 1.1522 17.9902 7.96 0.2331 2.1330 0.2553 1992.67

afrom AUTOAN2 b 0.693/13 c EX/N d [E(xi - 3-02/(N 1)]1 e (S.D./Mean) x 100 * 0.693/13Mean TableII.4aPharmaookinetic Parameters for Proxyphylline Following Two Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

Rabbit 1311 as tab kela k12a k21a Vla Vi V2 CI AUC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 4/kg 1/kg 4/kg 4/kg/hr ug-hrind

P 0.1208 1.5119 5.74 0.22 0.59 0.82 0.2795 1.2790 0.9995 0.1545 889.12

NH 0.2030 9.3596 3.41 0.83 6.44 2.30 0.3025 1.0974 0.7949 0.2228 617.14

I 0.2146 3.8892 3.23 0.51 1.97 1.62 0.5038 1.0848 0.5810 0.2328 1161.72

Meanc 0.1795 4.9202 3.86* 0.52 3.00 1.58 0.3619 1.1537 0.7918 0.2034 889.33

SDO 0.0511 4.0242 0.31 3.06 0.74 0.1234 0.1087 0.2093 0.0426 272.29

%CVe 28.49 81.79 58.68 101.93 46.89 34.10 9.42 26.43 20.86 30.62

Range 0.1208- 1.5119- 3.23- 0.22- 0.59- 0.82- 0.2795- 1.0848- 0.5810- 0.1545-617.14-

0.2146 9.3596 5.74 0.83 6.44 2.30 0.5038 1.2790 0.9995 0.2328 1161.72

a from AUTWOR b 0.693/0 C d (1:(x1 - 702/(N - 1)11 e (S.D./Mean) x 100 * 0.693 /0 Mean Table II.4b Pharmaookinetic Parameters for Proxyphylline Following Three Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

Rabbit oa as a 413 Via Vd Cl AUC Inventory code hr-1 hr-1 hr-1 hr L/kg L/kg L/kg/hr lighr/m1

II 0.1737 0.4767 17.7737 3.99 0.2365 1.0109 0.1756 769.91

J 0.1204 0.7028 10.2935 5.76 0.3067 2.0394 0.2455 1193.58

SS 0.0750 0.5356 11.6850 9.24 0.2533 1.9305 0.1448 947.78

Meanc 0.1230 0.5717 13.2507 5.63* 0.2655 1.6603 0.1886 970.42

SDd 0.0494 0.1173 3.9783 0.0367 0.5650 0.0516 212.74

%CVe 40.16 20.52 30.02 13.81 34.03 27.36 21.92

Range 0.0750- 0.4767-10.2935-3.99- 0.2365- 1.0109- 0.1448-769.91-

0.1737 0.7028 17.7737 9.24 0.3067 2.0394 0.2455 1193.58

a from AUTOAN2 b 0.693/a c EX/N d [E(xi R)2/(N 1)ll rn e (S.D./Mean) x 100 * 0.693/aMean Table 11.5 Pharmacokinetic Parameters for Proxyphylline After Administering Aminophylline (40mg/kg Intravenous Infusion over 30 min) Followed by Proxyphylline (135 mg/kg Leading Dose Intravenously over 5 min and 15 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hr) in Rabbits

Rabbit Ea 41) Inventory code hr-1 hr-1

BE 0.1820 3.81

B 0.1953 3.55

BV 0.1926 3.60

H 0.1950 3.55

G 0.2182 3.18

W 0.2348 2.95

Meanc 0.2030 3.41*

SDO 0.0196

fiCVe 9.65

Range 0.1820- 2.95-

0.2348 3.81

afrom NDNLIN b0.693/0 c EX/N d IE(xi 2)2/(N e (S.D./Mean) x 100 * 0.693/0 Mean 68 macokinetics of proxyphylline. Total xanthine plasma concentrations of theophylline plus proxyphylline reached about 1,000 mcg/ml (Figures II.la and II.lb) but no toxicities were observed. Earlier work in our laboratories has determined that theophylline plasma concentrations of 100 lig/m1 make the rabbits nervous and jumpy while concentrations of 250 to 400 ug/ml are fatal. Thus, bolus intravenous proxyphylline can be administered even if a full therapeutic "load" of theophylline is present without expected additive toxicity in rabbits. Further work is needed to determine if similar results will occur in humans. 69

CONCLUSION

Proxyphylline and theophylline pharmacokinetics in rabbits when administered concomitantly do not differ from those when administered alone. There were no apparent additive toxicities in the doses studied. These results suggest that proxyphylline and theophylline could be administered concomitantly without complications. However, further study with larger populations and in humans are necessary before it can be concluded that concomitant administration of the drugs is clinically safe. 70

ENDNOTES

1. Proxyphylline, 13-hydroxypropyltheophylline. Sigma

Chemical Company. St. Louis, MO.

2. Aminophylline injection USP 250 mg (25 mg/ml). Abbott

Laboratories. North Chicago, IL

3. a-hydroxyethyltheophylline. Sigma Chemical Company.

St. Louis, MO. 71

REFERENCES

1. J. Zuidema and F.W.H.M. Merkus, "Clinical and biophar-

maceutical aspects of theophylline and its

derivatives," Curr. Med. Res. Opin., 6, Suppl. 6,

14(1979).

2. J.G.R. Ufkes, R.S. Leeuwin, M. Ottenhof, A. Zeegers and J. Zuidema, "Efficacy of Theophylline and its N-7-substituted Derivatives in Experimentally Induced

Bronchial Asthma in the Guinea Pig," Arch. int.

Pharmacodyn., 253, 301 (1981).

3. K. Selvig and K.S. Bjerve, "Determination of Serum Proxiphylline by High-Pressure Liquid Chromatography," Scand. J. Clin. Lab. Invest. 37, 373 (1977).

4. "Neo-Biphyllin," Unlisted Drugs, Vol. 31, No.4, 58

(1979).

5. "Neo-Biphyllin," Unlisted Drugs, Vol. 28, No. 10, 178

(1976).

6. E. Joos, A. Seebach and M. Scherrer, "Gekreurter Doppeltblindversuch Mit Neophylline oral (Proxyphyllin

and Diprophyllin) bei Asthma Bronchiale," Schweiz.

Med. Wschr. 109, Nr. 19 (1979).

7. F.E. Roth, M.M. Winbury and W.M. Govier, Hydroxypropyltheophylline A Pharmacological Comparison 72

with Other Theophylline Preparation," J. Pharmacol.

Exp. Therap., 121, 487 (1957).

8. K. Selvig, "Pharmacokinetics of Proxyphylline in Adults After Intravenous and Oral Administration,"

Eur. J. Clin. Pharmacol., 19, 149 (1981).

9. L.E. Boardman, "Interactions Between Theophylline and

Theophylline Derivatives in Producing Relaxation of

Guinea Pig Isolated Trachial Chains," Br. J.

Pharmacol., 70, 120 (1980).

10. K. Svedmyr, T. Mellstrand and N. Svedmyr, "A Comparison Between Effects of Aminophylline,

Proxyphylline and Terbutaline in Asthmatics," Scand.

J. Resp.. Dis., Suppl. 101, 139 (1977).

11. C. Tivenius, "Comparison of Drugs for Asthma," Br.

Med. J., 2:733 (1971).

12. K. Selvig and K.S. Bjerve, "Metabolism of Proxyphylline in Man, Isolation and Identification of

Metabolites in Urine," Drug Metab. Dis., Vol. 8, No.

6, 456 (1980).

13. J.C.K. Loo and S. Riegelman, "Assessment of Pharmacokinetic Constants for Postinfusion Blood

Curves Obtained After I.V. Infusion, J. Pharm. Sci.,

Vol 59, No. 1, 53 (1970). 73

CHAPTER III

DYPHYLLINE AND THEOPHYLLINE

PHARMACOKINETICS WHEN ADMINISTERED

CONCOMITANTLY 74

ABSTRACT

Dyphylline and theophylline were given alone and concomitantly to rabbits. Theophylline plasma concentration time curves were best described as a one compartment open model for some subjects and a two compartment open model for the others with mean half-lives of 5.9 and 6.2 hr and

Vd of 0.94 and 1.03 L/kg, respectively, when administering aminophylline followed by dyphylline. When aminophylline was administered following dyphylline, the meanhalf-lives were 3.63 and 3.03 hr with Vd of 0.58 and 0.60L/kg for rabbit data best described as a one or two compartment open model respectively. Overall analysis of variance and Kruskal-Wallis test showed that differences among f3 and Vd for theophylline in different treatments were not statistically significant at a = 0.05. Dyphylline plasma concentrations for bolus dyphylline were fitted by either a two or three compartment openmodel with mean half-lives of 0.57 and 1.25 hr and Vd of 0.63 and

1.49 L/kg respectively and mean half-lives of 0.73 (two compartment) and 1.55 hr (three compartment) with Vd of

0.97 (two compartment) and 1.30 L/kg (three compartment) when followed by aminophylline. Dyphylline given as a 75 bolus loading dose with an infusion maintenance dose in the presence of aminophylline had a mean half-life of 1.43 hr.

Kruskal-Wallis test showed significant differences among the f3for different treatments( a< 0.05). Theophylline may have an effect on dyphylline elimination rate when administered concomitantly. 76

INTRODUCTION

Dyphylline, dihydroxypropyl theophylline, an N-7 substituted theophylline bronchodilator was introduced in

1946 to improve water insoluble and decrease toxicity relative to theophylline (1). Dyphylline does not release theophylline in vitro or in vivo (2). Apart from theophylline salts, dyphylline is the only theophylline derivative being used in the treatment of asthma in the United States. Dyphylline products are available commercially in many different pharmaceutical preparations such as tablets, sustained release tablets, intramuscular injections and suppositories (3). It is also available in combination with other xanthines, outside the

United States, such as theophylline, proxyphylline, or theophylline and proxyphylline (4-6). Pharmacokinetics, pharmacological actions and toxicities have been studied for dyphylline. In comparative animal studies the effective dyphylline dose is at least six times that of theophylline in order to produce the same pharmacological responses (7). In other studies, dyphylline is reported to be ten times less potent than theophylline (8,9). Dyphylline is nine times less potent than theophylline in relaxing the guinea pig trachea (10). 77

However, the plasma concentration reported to be effective in people is the same as for theophylline, 12 11g/m1 (9).

Hudson et al reported for aminophylline and dyphylline administered separately in twelve asthmatic patients, that a single dose of 1000 mg of dyphylline produced 16.3 mcg/ml in plasma which is the concentration necessary to produce a significant bronchodilation effect, compared to placebo (8).

Dyphylline half-life in humans was reported to be 1.7-2.0 hrs (1,2) which is fairly short when compared to theophylline. In most previous studies only a single dose was administered. Since dyphylline is eliminated from the body so quickly (ti=2 hr), the duration of effective dyphylline plasma concentration is not long enough to produce many pharmacological actions. In fact, the effect may have been so brief that it was missed in some studies.

This could explain some, but not all, of the conflicting reports which state that dyphylline is or is not an effective bronchodilator. The lethal intraperitoneal dyphylline dose in mice is

6 to 8 times that of theophylline (7). Thus, dyphylline is relatively nontoxic compared to theophylline (11). It is better tolerated in both oral and intramuscular injection forms with very mild toxicity (12). Dyphylline use has been popular in children and as an alternative to aminophylline in patients who are allergic to the ethylene diamine moiety of aminophylline (13). 78

Dyphylline, unlike theophylline, is primarily eliminated by glomerular filtration. At least 80% is excreted unchanged in the urine (2,14). Dyphylline is not hydro- lyzed or metabolized to theophylline (9). It has been stated in the Physician's Desk Reference that aminophylline should not be administered concurrently with other xanthine preparations (3). This is presumably to prevent additive or synergistic toxicities. However, it may be desirable in some clinical situations to administer dyphylline to patients who are concurrently receiving theophylline or theophylline salts without waiting for theophylline to be cleared from the body or to switch patients from dyphylline to aminophylline or aminophylline to dyphylline. This study was undertaken to investigate the pharmacokinetic behavior and gross toxicity of theophylline and dyphylline when given alone and concurrently in rabbits. 79

MATERIALS AND METHODS

Female New Zealand white rabbits weighing 2.17-3.20 kg were used in this study. Six rabbits each were used in each treatment. The materials and methods for preparation of solutions for injection, preparation of the rabbits, blood sample collection and sample collection and sample storage were the same as described in the materials and methods in Chapter 1.

Drug Administration Treatments

Treatment 1: same as Treatment 1 in Chapter I.

Treatment 2: 300 mg/kg of dyphyllinel (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 8 min.

Treatment 3: 40 mg/kg of aminophylline2 in 6.3 ml of solution was administered by intravenous infusion at the rate of 0.21 ml/min over 30 min. Then 30 min after stopping aminophylline, 300 mg/kg of dyphylline (100 mg/m1) was administered by intravenous infusion atthe rate of

1.02 ml/min over 8 min, followed by a maintenance dose of 100 mg/kg/hr of dyphylline was administered at the rate of

0.23 ml/min over 2 hours.

Treatment 4: 300 mg/kg of dyphylline (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 80 ml/min over 8 min. Then 30 mins after stopping dyphylline,

40 mg/kg of aminophylline in 6.3 ml of solution was administered by intravenous infusion at the rate of 0.21 ml/min over 30 mins.

Assay Plasma samples were collected, stored and analysed by the same methods as described in Chapter I. The internal standard used was 8-hydroxypropyltheophylline3. Data were also analysed by the same procedures as in Chapter I. 81

RESULTS AND DISCUSSION

Theophylline plasma concentration vs. time curves for six rabbits each following administration of aminophylline alone, aminophylline followed by dyphylline or dyphylline followed by aminophylline are shown in Figures I.1, III.la, and III.2b respectively. Data are essentially superimposable for all three figures. Typical individual plasma concentration curves after the same treatments are shown in

Figures 1.4, 111.3 and 111.4. Theophylline plasma concentration time profiles when administering aminophylline alone were all well fitted by a two compartment open model as discussed in Chapter I. Four of the six theophylline plasma concentration vs. time curves when adminstering aminophylline followed by dyphylline were also well fitted by a two compartment open model, as determined by AUTOAN2

(Table III.lb). The other two were best described by a one compartment open model (Table III.la). Only two of six theophylline plasma concentration time curves, when administering dyphylline followed by aminophylline, were best fitted by a two compartment open model (Table III.2b). The other four were best described by a one compartment open model (Table III.2a). Pharmacokinetic parameters for theophylline after administering aminophylline alone (Table I.1) 82

1000.00

0 100.00 0

10.00

.00 .00 4.00 6.00 .00 10.00 d.00 14.00 HOURS

Figure III.la Plasma concentration time curves for theophylline after administration of aminophylline (40 mg/kg intravenous infusion over 30 min) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 min) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hrs) in 6 rabbits. 83

10000.00

1000.00 X CD X

Zo 100.00

U) a. 10.00

.00 .00 .00 00 40 1.00 1 .00 HOURS

Figure III.lb Plasma concentration time curves for dyphylline after administration of aminophylline (40 mg/kg intravenous infusion over 30 min) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 min) and dyphylline maintenance dose (100 mg/ kg/hr over 2 hrs) in 6 rabbits. 84

1000.00

10.00

.00 .00 .00 -.00 .00 10.00 HOURS

Figure III.2a Plasma concentration time curves for dyphylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in 6 rabbits. 85

1000.00

I 100.00 I0

10.00

.00 .00 .00 -.00 .00 HOURS

Figure III.2b Plasma concentration time curves for theophylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 min) followed by aminophylline (40 mg/kg intravenous infusion over 30 min) in 6 rabbits. 86

1000.00

0 100.00

10.00

.00 .00 .00 .00 .00 10.00 1 .00 1 .00 HOURS

Figure 111.3 Plasma concentration time curve for theophylline (0) and dyphylline () after administration of aminophylline (40 mg/kg intravenous infusion over 30 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in subject UU. 87

1000.00

X 100.00 C.)X

10.00

.00 .00 .00 -.00 .00 .00 1 .00 1 .00 HOURS

Figure 111.4 Typical plasma concentration time curves for theophylline (0) and dyphylline (v) after administration of dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by aminophylline (40 mg/kg intravenous infusion over 30 minutes)in subjectW. Table III.la Pharmacokinetic Parameters for Theophylline Following One Compartment Open Model Behavior After Administering Aminophylline (40 mg/kg Intravenous Infusion over 30 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Rabbit kela tib Vda C1 AUC Inventory code hr-1 hr L/kg L/kg/hr u ghr/ml

UU 0.155 4.47 0.6371 0.0988 332.1601

L 0.096 7.22 1.2480 0.1199 278.3067

afrom AUTOAN2 b 0.693/0 Table III.lbPharmacokinetic Parameters for Theophylline Following Two Compartment Open Model Behavior After Administering Aminophylline (40 mg/kg Intravenous Infusion over 30 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

ua 4b Rabbit oa kela k12a kaa Via V2 Cl AUC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 Wkg L/kg L/kg L/kg/hr pghr/m1

VV 0.0344 0.8281 20.15 0.14 0.50 0.43 0.4382 1.0240 0.5858 0.0613 944.44

R 0.1481 6.9863 4.68 0.30 3.24 3.03 0.2288 0.4845 0.2557 0.0682 451.57

E 0.1361 0.8316 5.09 0.20 0.20 0.49 0.5300 0.7873 0.2573 0.1060 309.54

C 0.1307 3.4189 5.30 0.22 1.30 1.92 1.6522 1.8087 0.1565 0.3925 134.85

Meanc 0.1123 3.0162 6.17* 0.22 1.31 1.47 0.7123 1.0261 0.3138 0.1570 460.10

sod 0.0525 2.9146 0.07 1.37 1.25 0.6392 0.5665 0.1873 0.1582 347.91

%CVe 46.71 96.63 30.74 104.42 84.95 89.73 55.21 59.70 100.78 75.62

Range 0.0344- 0.8281- 4.68- 0.14- 0.20- 0.43- 0.2288- 0.4845- 0.1565- 0.0613- 134.85-

0.1481 6.9863 20.15 0.30 3.24 3.03 1.6522 1.8087 0.5858 0.3925 944.44

a from AUPDAN2 b 0.693/0 c d (E(xi 3)2/(N 1)0 e(S.D./Mean) x 100 * 0.693/Mean Table III.2aPharmaookinetic Parameters for Theophylline Following One Canpartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous over 8 min) Followed by Aminophylline (40 mg/kg Loading Dose Intravenously over 30 min) in Rabbits

Rabbit kela 4b vda c1 AUC Inventory code hr-1 hr-1 II/kg b/kg/hr ng.hr/m1

N 0.139 4.99 0.6335 0.0881 941.41

00 0.211 3.28 0.6216 0.1312 633.31

0 0.169 4.10 0.54900.0928 893.48

0.243 2.85 0.5041 0.1225 676.73

Meant 0.191 3.63* 0.5771 0.1087 786.23

SO 0.046 0.0613 0.0214 153.79

%CVe 23.98 10.63 19.69 19.56

Range 0.139- 2.85- 0.5041-0.0881- 633.31-

0.243 4.99 0.63350.1312 941.41

a from AUTOAN2 b 0.693/S c EX/W d D:lxi - 102/(N - e (S.D./Mean) x 100 * 0.693 /Mean Table III.2bPharmacokinetic Parameters for Theophylline Following Two Cbnpartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

V2 Cl RUC Rabbit Ra as tib kela k12a k21a Vla Vd Inventory pg-hr/m1 code hr-1 hr-1 hr hr -1 hr-I hr-I L/kg L/kg L/kg L/kg/hr

89.8087 0.4670 1.5657 1.48 0.73 0.25 0.63 0.3656 0.6395 0.2739 0.2680 0.0871 387.1618 W 0.1516 5.5966 4.57 0.29 2.50 2.76 0.3044 0.5521 0.2477

a from AUTO N2 b 0.693/0 92

included a mean elimination half-life of 5.2 hrs and a mean

volume of distribution (Vd) of 0.706 L/kg. Pharmacokinetic

parameters after administering aminophylline followed by

dyphylline are shown in Table III.la and III.lb for individual data which were fitted by a one or two compartment

open model, respectively. The mean kel for rabbits best fit by a one compartment open model is 0.126 hr-1 and the mean

S was 0.112 hr-1 for those best fitted by a two compartment

open model. Mean half-lives were 5.85 or 6.17 hrs. These values are not much different from each other or from the

parameters obtained when aminophylline was administered

alone 0.134 hr-1 and ti of 5.18 hrs). The mean Vd values were 0.943 and 1.026 L/kg which are 34% and 45%

greater than that of theophylline when aminophylline was

administered alone (0.706 L/kg). Pharmacokinetic parameters for theophylline when admi-

nistering dyphylline followed by aminophylline are shown in Table III.2a and III.2b when fitted to either a one or two

compartment open model, respectively. The mean kel for the one compartment data was 0.191hr-1 and the mean g for the

two compartment data was 0.309hr-1. These are greater

than for theophylline when aminophylline was administered

alone (0.134 hr-1). The mean theophylline half-lives of 3.63 hr (range of 2.85-4.99) and 3.03 hr (range of

1.48-4.57) are 30% and 42% shorter than the mean half-life of theophylline when aminophylline was administered alone 93

(5.18 hr, range of 3.98-7.17). Therefore, the presence of dyphylline may increase the elimination rate of

theophylline and shorten the elimination half-life of

theophylline. When dyphylline was administered in the presence of theophylline, the theophylline ti values were 6.17

(4.68-20.15) and 5.85 (4.47-7.22), which is not much dif-

ferent when comapared to administering aminophylline alone

(ti of 5.18 hrs). It may be that dyphylline enhances elimination of theophylline when theophylline is administered

in the presence of dyphylline, but dyphylline may not have

any effects when theophylline is already presentin the

plasma prior to dyphylline administration. However, the Kruskal-Wallis test showed that there are no statistically significant differences between R, Vd and AUC for

theophylline in these three different treatments (Table

I.1, III.la, III.lb, III.2a and III.2b). That is, the variation within treatment groups of six rabbits was so

large that differences in mean values of 40% are not sta-

tistically significant. Dyphylline plasma concentration time curves for each

of six rabbits when dyphylline was administered alone, dyphylline followed by aminophylline or aminophylline followed by dyphylline are shown in Figures 111.5, III.2a

and III.lb. Typical plasma concentration time curves for the same treatments are shown in Figures 111.3, 111.4 and

111.6. 94

1000.00

J 0 100.00 I0

10.00

.00 .00 -.00 40 10.00 HOURS

Figure III. 5 Plasma concentration time curves for dyphylline after administration of dyphylline (300mg/kg intravenous infusion over 8 minutes) in 6 rabbits. 95

1000.00

100.00

10.00

Figure 111.6 Typical plasma concentration time curve for dyphylline after administering dyphylline (300mg/kg by intravenous infusion over 8 min) in subject Z. 96

Dyphylline pharmacokinetic parameters when dyphylline was administered alone are shown in Table III.3a and

III.3b. Mean half-life of 0.57 hrs, mean Vd of 0.630 L/kg and mean clearance of 0.839 L/kg/hr are all close to those reported as 0.74 hrs, 1.008 L/kg and 0.942 L/kg/hr, respectively by Ng and Locock (15).

Tables III.4a and III.4b show dyphylline pharmacokinetic parameters when fitted by a two or three compartment open model when dyphylline was administered first and then followed by aminophylline. Table 111.5 shows the dyphylline 8 elimination rate and half-life when aminophylline was administered first followed by a dyphylline loading dose and a zero order maintenance dose. The Kruskal-Wallis test identified statistically significant differences among < 0.05), but no differences between Vd or AUC among these three treatments. Therefore, dyphylline Vd was not affected when administered concurrently with theophylline. Mean dyphylline ti when dyphylline was administered alone was 0.57 hr (0.46-0.64) or 1.25 hr (Tables III.3a and III.3b) whenfitted by a two or three compartment open model,respectively. When dyphylline administration was followed by theophylline, the mean dyphylline ti was 0.73 hrs(0.63-0.97) or 1.55 hr

(1.36-1.73) and the mean dyphylline ti for post infusion data following administration of aminophylline first, then a dyphylline loading dose, and then adyphylline main- Table III.3aPharmacokinetic Parameters for Dyphylline Following Two Compartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) in Rabbits

6a ea Rabbit tib kela k12a k21a Vla Vd V2 Cl RUC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 14/kg L/kg 1,/kg L/kg/hr pghr/al

VI 1.2496 7.7010 0.55 3.22 4.10 4.10 0.4435 0.7722 0.3287 1.4281 237.83

F 1.0875 5.0671 0.64 2.11 1.92 3.10 0.2348 0.6190 0.3842 0.4954 645.27

V2 1.1545 11.1866 0.60 3.66 4.51 3.26 0.1363 0.3776 0.2413 0.4989 433.41

Y 1.4944 13.1548 0.46 4.01 6.24 5.23 0.2389 0.6419 0.4030 0.9580 236.50

M 1.0886 8.4824 0.64 2.87 4.06 3.69 0.2836 0.7387 0.4551 0.8139 362.60

Meant 1.2149 9.1184 0.57* 3.17 4.17 3.88 0.2674 0.6299 0.3625 0.8389 383.12

SDd 0.1697 3.1383 0.74 1.54 0.85 0.1122 0.1549 0.0814 0.3859 169.03

we 13.97 34.42 23.19 36.9 21.94 41.95 24.59 22.46 46.00 44.12

Range 1.0875- 5.0671- 0.46-2.11- 1.92- 3.10- 0.1363-0.3776-0.2413- 0.4954-236.50-

1.2496 13.1548 0.64 4.01 6.24 5.23 0.4435 0.7722 0.4551 1.4281 645.27

a from AUTOANOR b0.693/4 c EX/N d (E (xi - 102/(N e (S.D./Mean) x 100 * 0.693/13Mean Table III.3b Pharmacokinetic Parameters for Dyphylline Following Three Compartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) in Rabbits

Rabbit Ba as ya tit) V1 Vd Cl AUC Inventory code hr-1 hr-1 hr-1 hr L/kg L/kg L/kg/hr pghr/MI

Z 0.5531 3.6344 15.0133 1.25 0.2312 1.4861 0.8219 279.21

afrom AUTCAN2 b 0.693/0 Table III.4aPharmacokinetic Parameters for Dyphylline Following Two Compartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

Rabbit oa aa tit) kela k12a k21a via Vd v2 Cl ADC inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 L/kg 1kg L/kg 1,/kg/hr pghr/mI

N 0.7110 5.8612 0.97 2.31 3.48 2.40 0.4104 1.0506 0.6402 0.9480 301.92

W 0.9372 10.5393 0.74 3.27 5.83 3.34 0.1502 0.4879 0.3377 0.4912 363.06

0 1.0347 7.7093 0.67 2.37 3.66 4.08 0.8118 1.5212 0.7094 1.9280 143.27

M 1.0975 11.6196 0.63 3.62 5.41 3.49 0.2585 0.8296 0.5711 0.9358 260.25

Means 0.9451 8.9324 0.73* 2.89 4.60 3.33 0.4077 0.9723 0.5646 1.0758 267.13

SDd 0.1694 2.6288 0.65 1.20 0.70 0.2898 0.4330 0.1615 0.6066 92.74

iCVe 17.93 29.43 22.64 26.05 20.90 71.07 44.53 28.60 56.39 34.72

Range 0.7110- 5.8612- 0.63- 2.31- 3.66- 2.40- 0.1502- 0.4879-0.3377- 0.4912- 143.27-

1.0975 11.6196 0.97 3.62 5.83 4.08 0.8118 1.5212 0.7094 1.9280 363.06

afrom AUTAN2 b 0.693/0 c EX/N d[:(xi - 212/(N e (S.D./Mean) x 100 0.693/0Mean Table III.4bPharmacokinetic Parameters for Dyphylline Following Three Compartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) Followed by Aminophylline (40 mg/kg Intravenous Infusion over 30 min) in Rabbits

Rabbit $ a a a a 4b Vi Vd Cl AtJC Inventory code hr-1 hr-1 hr-1 hr L/kg L/kg L/kg/hr pg-hr/m1

Y 0.3998 1.1577 10.4286 1.73 0.1945 1.3071 0.5227 365.96

W 0.5191 1.6495 18.98 1.36 0.1952 1.3112 0.6806 314.61

afrom AUTOAN2 b 0.693A Table 111.5 Pharmacokinetic Parameters for Dyphylline After Administering Amino- phylline (40 mg/kg Intravenous Infusion over 30 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits.

Rabbit 13a tib Inventory code hr-1 hr

C 0.2863 2.42

E 0.7519 0.92

L 0.3825 1.81

R 0.7087 0.98

UU 0.5450 1.27

W 0.2348 2.95

Meant 0.4894 1.43

SDd 0.2179

WVe 44.94

Range 0.2348 0.92-

0.7519 2.95

a from NONLIN b 0.69343 c EX/N d V(xi X)2/(N 1)0 e (S.D./Mean) x 100 * 0.693Mean 102 tenance dose, is 1.43 hr (0.92-2.95). From these findings one may conclude that when dyphylline is administered concurrently with theophylline, the dyphylline elimination half-life may be prolonged. This was unexpected because theophylline is a diuretic and, since dyphylline is mainly eliminated by the kidney (at least 82% excreted intact in the urine) (14), dyphylline ti should have been shortened in the presence of theophylline. Alternatively, the ti of dyphylline may increase as plasma concentrations increase. Poyner reported that dyphylline may exhibit dose dependent pharmacokinetics in dogs (16). Rabbits became "jumpy" and exhibited some minor muscular fasciculations at plasma theophylline concentrations of about 100 mcg/ml. Death preceeded by a generalized con- vulsion occurs at 250 to 400 mcg/ml as observed in our laboratory. Rabbits were also "jumpy" at dyphylline plasma concentration above 1000 mcg/ml. No serious toxicities were observed with concomitant aminophylline (theophylline plasma concentrations of 50-100 mcg/ml) and dyphylline bolus injection plus infusion (Figure III.la and III.lb) plasma concentrations maintained for 2 hours at 100 tO 800 mcg/ml. Total plasma methyl xanthine concentrations were above 1000 mcg/ml without apparent additive or synergistic toxicities. 103

CONCLUSION

Theophylline pharmacokinetics in rabbits when administered with dyphylline do not differ from those when administered alone. In this study the mean dyphylline elimination rate was statistically different when administered alone then when administered concurrently with theophylline. There were no apparent additive toxicities in the doses studied. Further study with larger populations and in humans are necessary before final conclusions can be drawn regarding pharmacokinetic interactions between these two methyl xanthines. 104

ENDNOTES

1. Dyphylline, dihydroxypropyltheophylline. Lemmon

Company, Sellersville, PA.

2. Aminophylline injection USP 250 mg (25 mg/ml). Abbott

Laboratories. North Chicago, IL.

3. Proxyphylline, fi-hydroxypropyltheophylline. Sigma

Chemical Company. St. Louis, MO. 105

REFERENCES

1. J. Zuidema and F.W.H.M. Merkus, "Clinical and

Biopharmaceutical Aspects of Theophylline and its

Derivatives," Curr. Med. Res. Opin., 6, suppl. 6, 14

(1979).

2. J. Zuidema and F.W.H.M. Merkus, "Pharmacokinetics and Pharmacodynamics of Diprophylline," Pharm. Weekbl.,

Sci. Ed., Vol. 3, No. 5, 1320 (1981).

3. "Physician's Desk Reference," Ed., Medical Economics Company, Oradell, N.J., 1982, pp.

4. "Neo-Biphyllin," Unlisted Drugs, Vol. 31, No. 4, 58

(1979).

5. "Neo-Biphyllin," Unlisted Drugs, Vol. 28, No. 10, 178

(1976).

6. L.E. Boardman, "Interactions between Theophylline and Theophylline Derivatives in Producing Relaxation of

Guinea Pig Isolated Tracheal Chains," Br. J.

Pharmacol., 70, 120 (1980).

7. J.D. McColl, J.M. Parker and J.K.W. Ferguson, "A Comparison of the Relative Toxic, Emetic and Convulsive Actions of a Series of Methylated Xanthine Derivatives," J. Pharmacol. Exp. Ther., 116, 343

(1956). 106

8. L.D. Hudson, J.L. Tyler and T.L. Petty, "Oral Aminophylline and Dihydroxypropyl Theophylline in

Reversible Obstructive Airway Disease: A Single-Dose,

Double-Blind, Crossover Comparison," Curr. Ther.

Res., 15, 367 (1973).

9. F.E.R. Simons, W. Blerman, A.C. Sprenkle and K.J.

Simons, "Efficacy of Dyphylline (dihydroxyprophyltheophylline) in Exercise-Induced

Bronchospasm," Peds. (suppl), 56, 916 (1975).

10. J.G.R. Ufkes, R.S. Leeuwin, M. Ottenhof, A. Zeegers and J. Zuidema, "Efficacy of Theophylline and its

N-7-Substituted Derivatives in Experimentally Induced

Bronchial Asthma in the Guinea Pig," Arch. Int.

Pharmacodyn., 253, 301 (1981).

11. P.V. Maney, J.W. Jones, E.G. Gross and H.M. Korus,

"Dihydroxypropyl Theophylline: Its Preparation and

Pharmacological and Clinical Study," J. Am. Pharm.

Assoc. 35, 266 (1946).

12. J.J. Ouellette, R.J. Kriz, J.B. Kooistra, "Efficacy and Tolerability of Dyphylline (Lufylline ®) in

Bronchial Asthma: A Retrospective Survey," Curr. Therap. Res., Vol. 27, No. 6, Section 1, 844 (1980).

13. C.T. Furukawa, G.G. Shapiro, W.E. Pierson and C.W. Bierman, "Dyphylline versus Theophylline: A Double

Blind Comparative Evaluation," J. Clin. Pharmacol.,

23, 414 (1983). 107

14. L.G. Gisclon, J.W. Ayres and G.H. Ewing, "Pharmacokinetics of Orally Administered Dyphylline,"

Am. J. Hosp. Pharm., 36, 1179 (1979).

15. P.K. Ng and R.A. Locock, "Comparative Pharmacokinetics of Theophylline and Dyphylline Following Intravenous

Injection in Rabbits," Research Communications in

Chemical Pathology and Pharmacology, Vol. 26, No. 3

(1979).

16. W.J. Poyner, "Dyphylline Pharmacokinetics Following Two Consecutive Intravenous Infusions in Beagle Dogs,"

Thesis in the University of Texas at Austin, Texas,

1980. 108

CHAPTER IV

ETOPHYLLINE, PROXYPHYLLINE AND

DYPHYLLINE PHARMACOKINETICS WHEN ADMINISTERED CONCOMITANTLY 109

ABSTRACT

Etophylline was given with proxyphylline or dyphylline in rabbits. Etophylline plasma concentration time curves were best described by both two and three compartment open model depending on individual subjects with mean half-lives of 1.71 and 3.74 hr and mean Vd of 1.05 and 2.16 L/kg when administering etophylline followed by proxyphylline; mean half-lives of 1.64 and 2.94 hr and mean Vd of 0.90 and 1.84

L/kg when administering etophylline followed by dyphylline. Etophylline mean half-lives of 2.20 and 1.54 hr were obtained when etophylline was administered following proxyphylline or dyphylline, respectively. Proxyphylline was given with etophylline or dyphylline. Proxyphylline plasma concentration time curves were described by a two compartment open model with a mean half-life of 3.15 hr and mean Vd of 1.05 L/kg when followed by etophylline; mean half-lives of 3.26 and 4.69 hr and mean Vd of 0.96 and 3.08 L/kg when administered followed by dyphylline. Proxyphylline mean half-lives of 3.27 and 3.11 hr were obtained when proxyphylline was administered following dyphylline or dyphylline, respectively. Overall, there were no significance differences among 8 and Vd for etophylline or proxyphylline, respectively, for different 110 treatments. Therefore, etophylline and proxyphylline pharmacokinetics were not changed when administered with one another or with dyphylline.

Dyphylline was administered with etophylline or proxyphylline. Dyphylline plasma concentration time curves were described by two or three compartment open models with mean half-lives of 1.05 and 1.12 hr and mean Vd of 0.89 and

0.64 L/kg when followed by etophylline; and mean half-lives of 1.11 hr with mean Vd of 0.80 L/kg when followed by proxyphylline. Dyphylline mean half-lives of 0.73 and 1.04 hr were obtained when administering dyphylline following etophylline or proxyphylline, respectively. Differences among dyphylline 8elimination rate were statistically

significant among treatments. Therefore, etophylline and proxyphylline affected dyphylline elimination rate when given concomitantly in rabbits. 111

INTRODUCTION

Theophylline has been widely used in the treatment of asthmatic patients since 1937. Because of its poor water solubility and high toxicity, many salts and derivatives have been developed. One salt is aminophylline, the ethylene diamine salt of theophylline, which was developed in

1908. Among the N-7 derivatives of theophylline are etophylline (8- hydroxyethyltheophylline), proxyphylline

(a-hydroxypropyltheophylline) and dyphylline (dihydroxypropyitheophylline) which were developed in 1951,

1956 and 1946 respectively (1). Both the effectiveness of theophylline and its toxicity are related to plasma concentrations (2). Its narrow therapeutic window (10-20 pg/m1) causes complications in administration of the drug in emergency situations. Intravenous doses of aminophylline, given too rapidly, may cause adverse effects in the central nervous, cardiovascular and respiratory systems (3). Allergic reactions, aminophylline poisoning, and sudden deaths associated with rapid intravenous injections have been reported

(4). Some patients are sensitive to the ethylenediamine moiety of aminophylline and develop eczematoid dermatitis

(5). 112

Due to the above undesirable properites of theophylline and its ethylenediamine salt, the

N-7-substituted derivatives of theophylline mentioned may replace theophylline and its salts in clinical practice. Etophylline, proxyphylline and dyphylline have been reported to be less toxic but also less potent than theophylline in producing pharmacological actions. None of these N-7-substituted derivatives release theophylline in vitro or in vivo. Each has its own pharmacokinetics and pharmacodynamics (6-8). Dyphylline is the only theophylline derivative that is being used in the United

States. All these derivatives are being used outside the United States and are available in many pharmaceutical forms including tablets, sustained released tablets, injectable solutions and suppositories both alone and in combination. Commercial preparations contain theophylline, dyphylline and proxyphylline in oral, rectal and injectable forms

(9-11). Theophylline, etophylline and proxyphylline are all eliminated, at least partially, by biotransformation.

Unchanged portions and their metabolites are eliminated in the urine. 7-13% of theophylline (12), 20% of etophylline (13) and 21-29% of proxyphylline (14) are excreted unchanged in the urine. Unlike the others, more than 80% of dyphylline is excreted unchanged and elimination is mainly by glomerular filtration (15). Therefore, 113 dyphylline would be a drug of choice for asthmatic patients with liver disease or any physical status that would affect metabolism pathways. Theophylline, etophylline or proxyphylline would be the drug of choice for asthmatic patients with kidney diseases.

This study was undertaken to investigate the pharmacokinetic behavior and gross toxicity of all possible combinations when any two derivatives were given concomitantly. 114

MATERIALS AND METHODS

Female New Zealand white rabbits weighing 2.05-3.66 kg were used in this study. Six rabbits each were used in each treatment except for treatment 5 and treatment 6 where four rabbits each were used. The materials and methods for preparation of solutions for injection, preparation of the rabbits, blood sample collection and sample collection and sample storage were the same as described in the materials and methods in Chapter I.

Drug Administration Treatments

Treatment 1: Same as Treatment 2 in Chapter I.

Treatment 2: 150 mg/kg of etophylline) (50 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min. Then 30 min after stopping etophylline, 135 mg/kg of proxyphylline2 (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min, followed by a maintenance dose of 15 mg/kg/hr of proxyphylline at the rate of 0.23 ml/min over 2 hours.

Treatment 3: 150 mg/kg of etophylline (50 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min. Then 30 min after stopping etophylline, 300 mg/kg of dyphylline3 (100 mg/ml) was admi- 115 nistered at the rate of 1.02 ml/min over 8 min, followed by a maintenance dose of 100 mg/kg/hr of dyphylline at the rate of 0.23 ml/min over 2 hours.

Treatment 4: Same as Treatment 2 in Chapter II.

Treatment 5: 135 mg/kg of proxyphylline (100 mg/ml) was administered by intravenous infusion at the rate of

1.02 ml/min over 3-5 min. Then 30 min after stopping proxyphylline 150 mg/kg of etophylline (50 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min, followed by a maintenance dose of 30 mg/kg/hr of etophylline at the rate of 0.23 ml/min over 2 hours.

Treatment 6: 135 mg/kg of proxyphylline (100 mg/ml) was administered by intravenous infusion at the rate of

1.02 ml/min over 3-5 min. Then 30 min after stopping proxyphylline 300 mg/kg of dyphylline (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 8 min, followed by a maintenance dose of 100mg/kg/hr of dyphylline at the rate of 0.23 ml/min over 2 hours.

Treatment 7: same as Treatment 2 in Chapter II.

Treatment 8: 300 mg/kg of dyphylline (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 8 min. Then 30 min after stopping dyphylline,

150 mg/kg of etophylline (50 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min, followed by a maintenance dose of 30 mg/kg/hr of etophylline at the rate of 0.23 ml/min over 2 hours. 116

Treatment 9: 300 mg/kg of dyphylline (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 8 min. Then 30 min after stopping dyphylline, 135 mg/kg of proxyphylline (100 mg/ml) was administered by intravenous infusion at the rate of 1.02 ml/min over 3-5 min, followed by a maintenance dose of 15 mg/kg/hr of proxyphylline at the rate of 0.23 ml/min over 2 hours.

Assay Plasma samples were collected, stored and analysed by the same methods as described in Chapter I. The internal standard used was theophylline.4 Data were also analysed by the same procedures as in Chapter I. 117

RESULTS AND DISCUSSION

Etophylline plasma concentration time curves following administration of etophylline alone, etophylline followed by proxyphylline, proxyphylline followed by etophylline, etophylline followed by dyphylline and dyphylline followed by etophylline are shown in Figures 1.7, IV.la, IV.3b,

IV.5a and IV.7b respectively and pharmacokinetic parameters for the same treatments are shown in Tables I.4a, I.4b,

IV.la, IV.lb, IV.3a, IV.3b, IV.6 and IV.11. Overall, Kruskal-Wallis test shows no significant dif-

ference among etophylline Vd and AUC (p < 0.05).

Therefore, one may conclude that proxyphylline or dyphylline has no effects on etophylline pharmacokinetic behavior when administered concurrently.

Proxyphylline palsma concentration time curves following administration of proxyphylline alone,

proxyphylline followed by etophylline, etophylline followed by proxyphylline, proxyphylline followed by dyphylline and dyphylline followed by proxyphylline are shown in Figures

11.4, IV.3a, IV.lb, IV.9a and IV.11b, respectively and pharmacokinetic parameters for the same treatments are

shown in Tables II.3a, II.3b, IV.5, IV.2, IV.7, IV.8 and

IV.13. 118

1000.00

I 0 100.00

10.00

.00 .00 .00 .00 .00 10.00 1 .00 1 .00 HOURS

Figure IV. la Plasma concentration time curves for etophylline after administering etophylline (15C mg/kg intravenous infusion over 5 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose(15 mg /kg /hr intravenous infusion over 2 hours) in 6rabbits. 119

1000.00

Jx 100.00

10.00

.00 .00 .00 10.00 1 .00 1 .00 HOURS

Figure IV. lb Plasma concentration time curves for proxyphylline after administering etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose(15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 120

1000400

100.00

10.00

.00 .00 -.00 .00 HOURS

Figure IV.2 Typical plasma concentration time curves for etophylline (*) and proxyphylline (0) after administering etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours). 121

1000.00

0 100.00 0 X 0 z 0 0 X U) C 10.00 -J CL

.00 2.00 4.00 6.00 6.00 10410 1.00 1400 HOURS

Figure IV.3a Plasma concentration time curvesfor proxyphylline after administrationof proxyphylline (135 mg/kg intravenous infusion over5 minutes) followed by etophylline loadingdose (150 mg/kg intravenous infusion over 5minutes) and etophylline maintenance dose (30 mg/kg/hrintravenous infusion over 2 hours) in 4 rabbits. 122

1000.00

3 X co 100.00 C.)

10.00

.00 00 .00 -.00 .00 10.00 1 .00 1 .00 HOURS

Figure IV.3b Plasma concentration time curves for etophylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 4 rabbits. 123

1000.00

100.00

10.00

.00 .00 .00 -.00 00 1.00 1 00 1 .00 HOURS

Figure IV.4 Typical plasma concentration time curves for proxyphylline (0) and etophylline (*) after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) and etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in subject GG. 124

1000.00

100.00 IU

10.00

.00 .00 -.00 .00 10.00 1 .00 14.00 HOURS

Figure IV.5a Plasma concentration time curves for etophylline after administration of etophylline (15C mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 125

1000.00

X 100.00 C.>

10.00

.00 .00 .00 -.00 .00 10.00 I .00 HOURS

Figure 1V.5b Plasma concentration time curves for dyphylline after administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 126

1000.00

cD 100.00

10.00

.00 .00 .00 .00 1 .00 1 .00 HOURS

Figure IV.6 Typical plasma concentration time curves for etophylline (*) and dyphylline (v) after the administration of etophylline (150 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg /kg /hr intravenous infusion over 2 hours) in subject XX. 127

10000.00

1000.00 IJ ° I

10.00

.00 .00 .00 -.00 .00 10.00 1 .00 1 .00 HOURS

Figure IV.7a Plasma concentration time curves for dyphylline after administering dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusionover 2 hours) in 6 rabbits. 128

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10.00

.00 .00 .00 -.00 .00 10.00 1 .00 1 .00 HOURS

Figure I17.7b Plasma concentration time curves for etophylline after administration dyphylline (30C mg/kg intravenous infusion over 8 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 129

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I3 100.00 I0 0 0 I 10.00 a.

.00 .00 .00 00 .00 10.00 2. 00 1 .00 HOURS

Figure IV.8 Typical plasma concentration time curves for dyphylline (v) and etophylline (It) after administering dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by etophylline loading dose (150 mg/kg intravenous infusion over 5 minutes) and etophylline maintenance dose (30 mg/kg/hr intravenous infusion over 2 hours) in subject X. 130

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0 100.00 0 I

10.00

AO 440 440 440 640 10.00 17.00 14.00 HOURS

Figure IV.9a Plasma concentration time curves for proxyphylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) ir 4 rabbits. 131

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1000.00 X 0a' X

Z 100.00

-J

10.00

.00 .00 .00 -.00 40 10.00 1 .00 1 .00 HOURS

Figure 1V.9b Plasma concentration time curves for dyphylline after administration of proxyphylline (135 mg/kg intravenous infusion over 5 minutes) followed by dyphylline loading dose (300 mg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in 4 rabbits. 132

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0moo 0

C) 2E C) C)

10.00 _J CL

40 .00 .00 -.00 40 1'.00 1 .00 1 .00 HOURS

Figure IV. 10 Typical plasma concentratior time curves for proxyphylline (0) and dyphylline (iv) after administration of Proxyphylline (135 mg/kg intravenous infusion over 5 minutes) and dyphylline loading dose (30Cmg/kg intravenous infusion over 8 minutes) and dyphylline maintenance dose (100 mg/kg/hr intravenous infusion over 2 hours) in subject YY. 133

10000.00

1000.00 -J 0 0 I U 6 100.00

C.) I co

-J 10.00

.00 .00 .00 -.00 .00 10.00 1 .00 1 .00 HOURS

Figure IV.11aPlasma concertration time curves for dyphylline after administration of dyphylline (30C mg/kgintravenous infusion over P minutes) followed by proxphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 134

1000.00

0 100.00 C)

10.00

.00 .00 .00 -.00 .00 10.00 1 .00 1 .00 HOURS

Figure IV.11b Plasma concentration time curves for proxyphylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 minutes) followed by proxyphylline loading dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 mg/kg/hr intravenous infusion over 2 hours) in 6 rabbits. 135

1000.00

z 0 100.00

I N 10.00

.00 00 00 .00 1' 00 1 .00 1 .00 HOURS

Figure IV. 12 Typical plasma concentration time curves for dyphylline (7) and proxyphylline after administration of dyphylline (300 mg/kg intravenous infusion over 8 minutes) and proxyphylline loaeing dose (135 mg/kg intravenous infusion over 5 minutes) and proxyphylline maintenance dose (15 me /kg /hr intravenous infusion over 2 hours) in subject Z. Table IV.laPharmacokinetic Parameters for Etophylline Following TWo Compartment Open Model Behavior After Administering Etophylline (150 mg/kg Intravenous Infusion over 5 min) Followed by Proxyphylline (135 mg/kg Loading Dose Intravenously over 5 min and 15 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Rabbit oa a tib kela k12a k2la via Vd V2 Cl AUC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 I,/kg L/kg 11k9 L1/kg/hr pg-hr/m1

U 0.3905 14.0715 1.77 1.55 10.50 4.07 0.3480 1.1336 0.7856 0.5394 369.00

AA 0.4430 7.5390 1.56 0.97 5.22 4.97 0.4122 0.7759 0.3637 0.3990 360.92

JJ 0.3828 9.3071 1.81 0.83 3.71 3.60 0.6421 1.2354 0.7057 0.5297 345.18

Meanc 0.4054 10.3059 1.71* 1.12 6.48 4.21 0.4674 1.0483 0.6183 0.4894 358.37

SDd 0.0328 3.3788 0.38 3.57 0.70 0.1546 0.2413 0.2241 0.0784 12.11

8CVe 8.08 32.79 34.08 55.02 16.54 33.08 23.02 36.25 16.02 3.38

Range 0.3828- 7.5390-1.56 0.83- 3.71 3.60- 0.3480- 0.7759- 0.3637-0.3990- 345.18-

0.4430 14.0715 1.81 1.55 10.50 4.97 0.6421 1.2354 0.7856 0.5394 369.00

a from AMANOR b 0.693/0 C EX/N d 0 lxi - i)2/(N - 1)1i e (S.D./Mean) x 100 * 0.693/3 Mean Table IV.lb?harmacokinetic Parameters for Etophylline Following Three Compartment Open Model Behavior After Administering Etophylline (150 mg/kg Intravenous Infusion over 5 min) Followed by Proxyphylline (135 mg/kg Loading Dose Intravenously over 5 min and 15 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Rabbit oa a a tab V1 Vd Cl AOC Inventory code hr-1 hr-1 hr-1 hr 14/kg 14/kg 14/kg/hr pg-hr/m1

CC 0.1946 0.9201 13.0464 3.56 0.3839 1.9414 0.3778 457.95

TT 0.2093 1.0967 11.9011 3.31 0.3878 2.1797 0.4513 359.32

CO 0.1518 1.1467 12.4871 4.57 0.3985 2.3675 0.3594 453.91

Meanc 0.1852 1.0545 12.4782 3.74* 0.3901 2.1629 0.3962 423.73

SOd 0.0299 0.1190 0.5727 0.0076 0.2135 0.0486 55.81

%CVe 16.13 11.29 0.0459 1.94 9.87 12.27 13.17

Range 0.1518- 0.9201-11.9011- 3.31- 0.3839- 1.9414-0.3594- 359.32-

0.2093 1.1467 13.0464 4.57 0.3985 2.3675 0.4513 457.95

a from AUTORN2 b 0.693/0 c EX/N d (E(xi - 1)2/(N - e (S.D./Mean) x 100 * 0.693/B Mean Table IV.2 Pharmacokinetic Parameters for Proxyphylline After Administering Eto- phylline (150 mg/kg Intravenous Infusion over 5 min) Followed by Proxyphylline (135 mg/kg Loading Dose Intravenously over 5 min and Proxyphylline Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits.

Rabbit Oa tib Inventory code hr -1 hr

U 0.2121 3.27

AA 0.1915 3.62

JJ 0.2388 2.90

CC 0.1700 4.08

Ti' 0.1837 3.77

QQ 0.2744 2.53

Meant 0.2118 3.27*

SDd 0.0390

%CVe 18.40

Range 0.1700- 2.90-

0.2744 4.08

afrom NDNLIN b 0.693/0 c EX/N d [E(xl - 1)2/(N - e (S.D./Mean) x 100 * 0.693/0Mban Table IV.3aPharmacokinetic Parameters for Etophylline Following Two Compartment Open Model Behavior After Administering Etophylline (150 mg/kg Intravenous Infusionover 5 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenouslyover 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Rabbit Ba a k21a via a tib kela k12a Vd V2 Cl ADC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr -1 L/kg L/kg L/kg Likg/hr aghr/m1

DD 0.5074 9.1526 1.37 1.34 4.44 3.22 0.4291 1.0394 0.6103 0.5750 312.18 TT 0.4316 18.7745 1.61 1.78 14.10 4.99 0.1922 0.7422 0.5500 0.3421 289.47 EE 0.2797 9.8269 2.48 1.09 6.34 2.49 0.1958 0.7874 0.5916 0.2134 569.82

XX 0.4337 14.8171 1.60 1.46 9.05 4.41 0.2398 0.8582 0.6184 0.3502 292.44 AA 0.4616 3.9654 1.50 1.01 2.83 3.13 0.6270 1.0562 0.4292 0.6333 307.18

Meanc 0.4228 11.3073 1.64*1.34 7.35 3.65 0.3368 0.8967 0.5599 0.4228 354.22

SO 0.0856 5.6748 0.31 4.43 1.02 0.1890 0.1441 0.0777 0.1754 120.91 %CVe 20.26 50.19 22.98 60.22 27.99 1.7819 16.07 13.88 41.49 34.13

Range 0.2797- 3.9654- 1.37- 1.01- 2.83- 2.49- 0.1922-0.7422-0.4292- 0.2134- 289.47 0.5074 18.7745 2.48 1.78 14.10 4.99 0.6270 1.0562 0.6184 0.6333 569.82

a from AUTOAN2 b 0.693/0 c EX/14 d IE(xi 31)2/(N 10 e (S.D./Mean) x 100 * 0.693/0Mean Table IV.3bPharmacokinetic Parameters for Etophylline Following Three Compartment Open Model Behavior After Administering Etophylline (150 mg/kg Intravenous Infusion over 5 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

y a Rabbit fi a as a tib V1 Vd Cl AUC Inventory code hr-1 hr-1 hr-1 hr L/kg L/kg L/kg/hr pg-hr/m1

BB 0.2361 0.9176 14.1531 2.94 0.3081 1.8374 0.4338 355.35

afrom AUTOAN2 b 0.6934 Table IV.4 Pharmacokinetic Parameters for Dyphylline After Administering Etophylline (150 mg/kg Intravenous Infusion over 5.0min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hrs) in Rabbits.

Rabbit oa tib Inventory code hr-1 hr

DD 1.1501 0.60

TT 1.0186 0.68

EE 0.6848 1.01

XX 1.0496 0.66

AA 0.8705 0.80

BB 0.8908 0.78

Meanc 0.9441 0.73*

SO 0.1641

liCVe 17.38

Range 0.6848- 0.60-

1.1501 1.01

a from MALIN b 0.693/$ c EX/N d (E(xi 102/(N 1))1 e (S.D./Mean) x 100 * 0.693/3Mean Table IV.5 Pharmacokinetic Parameters for Proxyphylline Following Two Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Etophylline (150 mg/kg Loading Dose Intravenously over 5 min and 50 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

as k21a Via Rabbit oa tib kela kl2a Vd V2 Cl AUC Inventory code hr-1 hr -1 hr hr -1 hr -1 hr -1 L/kg L/kg L/kg L/kg/hr V ghr/m1

KK 0.3126 14.7284 2.22 1.12 10.90 4.53 0.6036 1.6721 1.0685 0.6761 262.56

K 0.2248 8.9858 3.08 0.96 7.84 2.63 0.2645 0.7343 0.4698 0.2542 831.04

GG 0.1989 16.1883 3.48 0.74 13.40 5.12 0.3110 1.0091 0.6981 0.2286 702.62

II 0.1441 12.0049 4.81 2.78 6.61 7.45 0.5923 0.7939 0.2016 1.64661011.56

Meant 0.2201 12.9544 3.15* 1.40 9.69 4.93 0.4429 1.0524 0.6095 0.7014 701.95

sea 0.0702 3.2135 0.93 3.06 1.99 0.1802 0.4297 0.3672 0.6627 319.16

%CVe 31.92 24.81 66.65 31.60 40.29 40.68 40.83 60.24 94.48 45.47

Range 0.1441- 8.9858- 2.22- 0.74- 6.61- 2.63- 0.2645- 0.7343-0.2016- 0.2286- 262.56-

0.3126 16.1883 4.81 2.78 13.40 7.45 0.6036 1.6721 1.0685 1.6466 1011.56

afrom AUTO4N2 b 0.693/13 c EX/N d [E(xi - 2)2/(N 1)11 e (S.D./Mean) x 100 * 0.693/0Mean Table IV.6 Pharmacokinetic Parameters for Etophylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Etophylline (150 mg/kg Loading Dose Intravenously over 5 min and 30 mg/kg/hr Maintenance Dose by Intra- venous Infusion over 2 hours) in Rabbits.

Rabbit oa 413 Inventory code hr-1 hr

KK 0.3811 1.82

K 0.3512 1.97

GG 0.2414 2.87

II 0.2872 2.41

Meant 0.3152 2.20*

SO 0.0629

%Ce 19.96

Range 0.2414- 1.82-

0.3811 2.87

a from NDtx.IN b 0.693/0 c EX/N d [E(xi 11)2/(N 1)0 e (S.D./Mean) x 100 * 0.693/0Mean Table IV.7Pharmacokinetic Parameters for Proxyphylline Following Two Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

a 4b keia Rabbit a k12a k21a Vla Vd V2 Cl AOC Inventory code hr-1 hr hr-1 hr-1 hr-1 L/kg L/kg L/kg L/kg/hr pg-hr/m1

SS 0.2345 9.6606 2.96 8.22 6.73 2.92 0.2291 1.0434 0.7443 1.8832 564.66

I 0.2171 8.9728 3.19 7.73 6.47 2.91 0.2369 0.8514 0.6145 1.8311 758.39

YY 0.1865 7.6418 3.72 0.61 5.27 2.52 0.2841 0.9775 0.6934 0.1733 1004.34

Meanc 0.2127 8.7584 3.26* 5.52 6.16 2.78 0.2500 0.9574 0.6841 1.2959 775.80

Si 0.0243 1.0263 4.26 0.78 0.23 0.0298 0.0976 0.0654 0.9725 220.36

%CVe 11.42 11.72 77.16 12.64 8.21 11.90 10.19 9.56 75.05 28.40

Range 0.1865- 7.6418- 2.96- 0.61- 5.27- 2.52- 0.2291-0.8514-0.6145- 0.1733-564.66-

0.2345 9.6606 3.72 8.22 6.73 2.92 0.2841 1.0434 0.7443 1.8832 1004.34

a from AUTOAN2 b 0.693/4 c EX/N d V:(xi - 11)2/(N - 1))3 e (S.D./Mean) x 100 * 0.693/13Mean Table IV.8 Pharmacokinetic Parameters for Proxyphylline Following Three Compartment Open Model Behavior After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Rabbit Oa as ya 4b V1 Vd Cl AUC Inventory bode hr-1 hr-1 hr-1 hr L/kg L/kg L/kg/hr pghr/m1

A 0.1478 0.613310.7595 4.69 0.7318 3.0800 0.4552 317.50

afrom AUPDAN2 b 0.693A Table IV.9Pharmacokinetic Parameters for Dyphylline After Administering Proxyphylline (135 mg/kg Intravenous Infusion over 5 min) Followed by Dyphylline (300 mg/kg Loading Dose Intravenously over 8 min and 100 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Rabbit ea tib Inventory code hr-1 hr

SS 0.6877 1.01

I 0.8284 0.84

YY 0.6820 1.02

A 0.4591 1.51

Meanc 0.6643 1.04*

SO4 0.1526

%CVe 22.98

Range 0.4591- 0.84-

0.8284 1.51

a from NDNLIN b 0.693/0 c EX/N d 0 (x1 - 11)2/(N e (S.D./Mean) x 100 * 0.693/ Mean Table IV.10aPharmacokinetic Parameters for Dyphylline Following Two Compartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) Followed by Etophylline (135 mg/kg Loading Dose Intravenously over 5 min and 30 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

a a Rabbit Oa t4b kela k12a k2la via Vd V2 CI AUC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 L/kg 1kg L/kg I,/kg/hr p g.hr /m1

PP 0.4542 4.5391 1.53 1.75 3.44 1.84 0.3112 0.9959 0.6847 0.5446 486.67

X 0.8640 10.0308 0.80 2.08 3.61 3.05 0.3711 0.8285 0.4574 0.7719 341.97

VI 0.6197 6.9274 1.12 2.45 3.52 1.96 0.2864 0.9472 0.6608 0.7017 423.33

B 0.6685 11.2160 1.04 5.62 5.89 1.51 0.0850 0.6535 0.5685 0.4775 514.65

0 0.7072 6.9079 0.98 1.69 3.49 3.09 0.7961 1.0398 0.2437 1.3454 335.06

Meanc 0.6627 7.9242 1.05* 2.72 3.99 2.29 0.3700 0.8930 0.5230 0.7682 420.34

SDd 0.1482 2.6814 1.65 1.06 0.73 0.2614 0.1554 0.1799 0.3435 81.73

%CVe 22.36 33.84 60.67 26.66 31.92 70.64 17.40 34.41 44.72 19.44

Range 0.4542- 4.5391- 0.80- 1.69- 3.44- 1.51- 0.0850- 0.6535-0.2437-0.4775- 335.06-

0.8640 11.2160 1.53 5.62 5.89 3.09 0.7961 1.0398 0.6847 1.3454 514.65

a from AUTOAN2 b0.693/0 c EX/N d (E (xi 102/(N 1) 11 e (S.D./Mean) x 100 * 0.693A3Mean Table IV10b Pharmacokinetic Parameters for Dyphylline Following Three Compartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous over 8 min) Followed by Etophylline (135 mg/kg Loading Dose Intravenously over 5 min and 30 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

Rabbit aa a a 413 V1 Vd Cl AUC Inventory code hr-1 hr-1 hr-1 hr L/kg L/kg L/kg/hr pg-hr/m1

LL 0.6191 1.4883 16.1576 1.12 0.0770 0.63510.3931 557.98

a from AUTOAN2 b 0.693/0 Table IV.11 Pharmacokinetic Parameters for Etophylline after administering Dyphylline (300 mg/kg Intravenous Infusion over 5 min) Followed by Etophylline (150 mg/kg Loading dose Intravenously over 5 min and 30 mg/kg/hr Mainte- nance Dose by Intravenous Infusion over 2 hours) in Rabbits.

Rabbit oa tib Inventory code hr-1 hr

PP 0.2207 3.14

X 0.8118 0.85

0.3442 2.01

B 0.3656 1.90

0 0.4950 1.40

LL 0.4647 1.49

Meaner 0.4503 1.54*

SDd 0.2020

%CVe 44.86

Range 0.2207- 0.85-

0.8118 3.14

afrom NONLIN b 0.693/0 c DIM d (E(xi - 1)2/(N 1)11 e (S.D./Mean) x 100 * 0.693/Mean Table IV.12 Pharmacokinetic Parameters for Dyphylline Following Two Compartment Open Model Behavior After Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) Followed by Proxyphylline (135 mg/kg Loading Dose Intravenously over 5 min and 15 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hours) in Rabbits

a Rabbit oa tib kela k12a k21a V1a wi V2 CI AUC Inventory code hr-1 hr-1 hr hr-1 hr-1 hr-1 L/kg L/kg L/kg L/kg/hr pghr/m1

N 0.4819 4.8599 1.44 1.52 2.42 1.70 0.4281 1.1410 0.7129 0.6507 472.52

00 0.7617 11.2012 0.91 1.21 3.26 6.20 0.1151 0.7618 0.6467 1.3928 423.11

LL 0.6440 14.5920 1.08 5.43 8.16 1.75 0.0810 0.6034 0.5224 0.4397 398.52

Z 0.6541 11.9189 1.06 2.99 7.06 2.66 0.1608 0.7522 0.5914 0.4807 464.11

X 0.6424 7.3857 1.08 2.60 6.21 2.83 0.1594 0.6146 0.4552 0.4143 506.30

PP 0.5500 7.6197 1.22 2.07 4.86 2.38 0.2533 0.9456 0.6923 0.5244 435.83

Meanc 0.6224 9.5962 1.11* 2.64 5.33 2.92 0.1996 0.8031 0.6035 0.6504 450.07

Sod 0.0962 3.5820 1.52 2.22 1.67 0.1260 0.2070 0.1004 0.3731 38.60

%CVe 15.45 37.33 57.53 41.74 57.27 63.14 25.77 16.64 57.36 8.58

Range 0.4819- 4.8599- 0.91- 1.21- 2.42- 1.70- 0.0810-0.6034-0.4552- 0.4143- 398.52-

0.7617 14.5920 1.44 5.43 8.16 6.20 0.4281 1.1410 0.7129 1.3928 506.30

a from AUICAN2 b 0.693/0 c EX/N d (E(xi - 102/(N 1)1* e (S.D./Mean) x 100 * 0.693/0Mean Table IV.13Pharmacokinetic Parameters for Proxyphylline after Administering Dyphylline (300 mg/kg Intravenous Infusion over 8 min) Followed by Proxyphylline (135 mg/kg Loading DOse Intravenously over 5 min) and 15 mg/kg/hr Maintenance Dose by Intravenous Infusion over 2 hrs) in Rabbits.

Rabbit Oa tib Inventory code hr-1 hr

N 0.1604 4.32

00 0.2732 2.54

LL 0.2250 3.08

Z 0.2801 2.47

X 0.2097 3.30

PP 0.1888 3.67

Meant 0.2229 3.11*

SDd 0.0470

%CVe 21.09

Range 0.1604- 2.54-

0.2801 4.32

afrom NDNLIN b 0.693/8 c EX/N d(E(xi - 102/(N - e (S.D./Mean) x 100 * 0.693 /Mean 152

Overall Kruskal-Wallis test shows no significance difference among proxyphylline R, Vd and AUC (p < 0.05).

Therefore, one may conclude that etophylline or dyphylline have no effects on proxyphylline pharmacokinetic behavior when administered concurrently. Dyphylline plasma concentration time curves following administration of dyphylline alone, dyphylline followed by etophylline, etophylline followed by dyphylline, dyphylline followed by proxyphylline and proxyphylline followed by dyphylline are shown in Figures 111.2, IV.7a, IV.11a,

IV.9b, IV.4b, and pharmacokinetic parameters for the same treatments are shown in Tables III.3a, III.3b, IV.10a,

IV.10b, IV.4, IV.12 and IV.9. Overall Kruskal-Wallis test shows significant difference among the Relimination rate, but no significant differences among the volume of distribution and area under the curve. Mean dyphylline ti when administered alone and fitted by a two compartment open model was 0.57 hr (0.46-0.64)

(Table III.3a). Mean dyphylline ti when dyphylline was followed by etophylline and proxyphylline when fitted to two compartment open model are 84% and 95% (mean ti 1.05, range 0.80-1.53 and mean ti 1.11, range 0.91-1.44) greater than dyphylline ti when dyphylline was given alone. When dyphylline was administered in presence of etophylline and proxyphylline the half-lives were also prolonged by 28% and 153

83% (mean ti 0.73, range 0.60-1.01 and mean ti 1.04, range

0.84-1.51). Therefore, one may conclude that when etophylline or proxyphylline is administered concurrently with dyphylline, the elimination half-life of dyphylline is prolonged. Therefore, when dyphylline is to be given concurrently with etophylline or proxyphylline, complications might occur in predicting the elimination rate of dyphylline. Rabbits were "jumpy" at dyphylline plasma concentration above 1000 mcg/ml (Figures IV.9b and IV.11a).

The total xanthine concentrations for all the treatments, when given any two derivatives concurrently, were 1000 mcg/ml or above without any additive or synergistic toxicities. Therefore, etophylline, proxyphylline and dyphylline may be given concurrently to the total methyl xanthines concentration which produce pharmacological actions without any severe toxicities. 154

CONCLUSION

Etophylline, proxyphylline and dyphylline pharmacokinetics when all possible combinations of any two were given concomitantly in rabbits. Proxyphylline or dyphylline have no effects on etophylline pharmacokinetics when given concurrently. Etophylline or dyphylline have no effects on proxyphylline pharmacokinetics when given concurrently. Dyphylline elimination rate were prolonged when given concurrently with etophylline and proxyphylline.

Therefore, etophylline and proxyphylline may be given concurrently or switch from one to the other without waiting for one to be cleared off from the body, but dyphylline administration should be in caution when given concurrently with these two compounds. There were no apparent additive toxicities in doses studied. Further study with larger populations and in humans are necessary before it can be concluded that concomitant administration of the drugs is clinically safe. 155

ENDNOTES

1. Etophylline, 13-hydroxyethyltheophylline. Sigma

Chemical Company. St. Louis, MO.

2. Proxyphylline, Q-hydroxypropyltheophylline. Sigma

Chemical Company. St. Louis, MO.

3. Dyphylline, dihydroxyproyltheophylline. Lemmon

Company. Sellersville, PA.

4. Theophylline. Sigma Chemical Company. St. Louis, MO. 156

REFERENCES

1. J. Zuidema and F.W.H.M. Merkus, "Clinical and

Biopharmaceutical Aspects of Theophylline and its

Derivatives," Curr. Med. Res. Opin., 6, Suppl. 6, 14

(1979).

2. P.A. Mitenko and R.I. Ogilvie, Clin. Pharmac. Therp.,

16, 720 (1974).

3. "Physician's Desk Reference," Ed. Medical Economics Company, Oradell N.J., 1982, pp. 1754.

4. "Martindale, The Extra Pharmacopoeia," N.W. Blacow, Ed., 27th ed., Pharmaceutical Press, London, England,

1977, p. 279.

5. C.H. Lawyer, E.J. Bardana, R. Rodgers and N. Gerber, "Utilization of Intravenous Dihydroxypropyl

Theophylline (dyphylline) in an Aminophylline-Sensitive Patient, and its Phar-

macokinetic Comparison with Theophylline," J. Allergy

Clin. Immunol., Vol. 65, No. 5, 353 (1980).

6. J. Zuidema and F.W.H.M. Merkus, "Clinical and Biopharmaceutical Aspects of Theophylline and its

Derivatives," Curr. Med. Res. Opin., 6, suppl. 6, 14

(1979).

7. J. Zuidema and F.W.H.M. Merkus, "Pharmacokinetics and 157

Pharmacodynamics of Diprophylline," Pharm. Weekbl.,

Sci. Ed., Vol. 3, No. 5, 1320 (1981).

8. J.G.R. Ufkes, R.S. Leeuwin, M. Ottenhof, A. Zeegers and J. Zuidema, "Efficacy of Theophylline and its

N-7-substituted Derivatives in Experimentally Induced

Bronchial Asthma in the Guinea Pig," Arch. Int.

Pharmacodyn., 253, 301 (1981).

9. "Physician's Desk Reference," Ed., Medical Economics

Company, Oradell, N.J., 1982, pp.

10. "Neo-Biphyllin," Unlisted Drugs, Vol. 31, No. 4, 58

(1979).

11. "Neo-Biphylline," Unlisted Drugs, Vol. 28, No. 10,

178 (1976).

12. R.I. Ogilvie, "Clinical Pharmacokinetics of Theophylline," Clin. Pharm., 3, 267 (1978).

13. J. Zuidema, J. Verhoeven and F.W.H.M. Merkus, "Pharmacokinetics of Etophylline after Intravenous and

Oral Administration to Human," Int. J. Clin. Pharmacol., Vol. 19, No. 7, 310 (1981).

14. K. Selvig and K.S. Bjerve, "Metabolism of Proxyphylline in Man, Isolation and identification of

Metabolites in Urine,"Drug Metab. Dis., Vol. 8,

No. 6, 456 (1980).

15. L.G. Gisclon, J.W. Ayres and G.H. Ewing, "Pharmacokinetics of Orally Administered Dyphylline,"

Am. J. Hosp. Pharm., 36, 1179 (1979). 158

BIBLIOBRAPHY

Boardman, L.E., "Interactions Between Theophylline and Theophylline Derivatives in Producing Relaxation of Guinea Pig Isolated Trachial Chains," Br. J. Pharmacol., 70, 120 (1980).

El-Yazigi, A. and Sawchuk, R. J., "Theophylline Absorption and Disposition in Rabbits: Oral, Intravenous, and Concentration-Dependent Kinetic Studies," J. Pharm. Sci., Vol. 70, No.4 (1981).

"Evaluation of Drug Interactions," 2nd Ed., The American Pharmaceutical Association, Washington DC., 1976, p. 321. Furukawa, C.T., Shapiro, G.G., Pierson, W.E. and Bierman, C.W., "Dyphylline versus Theophylline: A Double Blind Comparative Evaluation," J. Clin. Pharmacol., 23, 414 (1983). Gisclon, L.G., Ayres, J.W. and Ewing, G.H., "Pharmacokinetics of Orally Administered Dyphylline," Am. J. Hosp. Pharm., 36, 1179 (1979).

Hudson, L.D., Tyler, J.L. and Petty, T.L., "Oral Aminophylline and Dihydroxypropyl Theophylline in Reversible Obstructive Airway Disease: A Single-Dose, Double-Blind, Crossover Comparison," Curr. Ther. Res., 15, 367 (1973). Jauch, R. and Zimmer, A., "Human Pharmacokinetic von Oxyathyltheophyllin and Fominoben HC1," Arzneim. Forsch., 28, 693 (1978). Joos, E., Seebach, A. and Scherrer, M., "Gekreurter Doppeltblindversuch Mit Neophylline oral (Proxyphyllin and Diprophyllin) bei Asthma Bronchiale," Schweiz. Med. Wschr. 109, Nr. 19 (1979). Lawyer, C.H., Bardana, E.J., Rodgers, R. and Gerber, N., "Utilization of Intravenous Dihydroxypropyl Theophylline (dyphylline) in an Aminophylline-Sensitive Patient, and its Pharmacokinetic Comparison with Theophylline," J. Allergy Clin. Immunol., Vol. 65, No. 5, 353 (1980).

Loo, J. C. K. and Riegelman, S., "Assessment of Pharmacokinetic Constants for Postinfusion Blood Curves Obtained After I.V. Infusion," J. Pharm. Sci., Vol 59, No. 1, 53(1970). 159

Maney, P.V., Jones, J.W., Gross, E.G. and Korus, H.M., "Dihydroxypropyl Theophylline: Its Preparation and Pharmacological and Clinical Study," J. Am. Pharm. Assoc. 35, 266 (1946).

"Martindale, The Extra Pharmacopoeia," N. W. Blacow, Ed., 27th ed., Pharmaceutical Press, London, England, 1977, p. 279. McColl, J.D., Parker, J.M. and Ferguson, J.K.W., "A Comparison of the Relative Toxic, Emetic and Convulsive Actions of a Series of Methylated Xanthine Derivatives," J. Pharmacol. Exp. Ther., 116, 343 (1956).

Mitenko, P. A. and Ogilvie, R. I., "Rational Intravenous Doses of Theophylline," N. Engl. J. Med., 289, 600(1973). Mitenko, P. A. and Ogilvie, R. I., Clin. Pharmac. Therp., 16, 720 (1974). Ng, P. K. and Locock, R. A., "Comparative Pharmacokinetics of Theophylline and Dyphylline Following Intravenous Injection in Rabbits," Research Communications in Chemical Pathology and Pharmacology, Vol. 26, No. 3 (1979). Ogilvie, R. I., "Clinical Pharmacokinetics of Theophylline," Clin. Pharm. 3: 267 (1978).

Ouellette, J.J., Kriz, R.J., and Kooistra, J.B., "Efficacy and Tolerability of Dyphylline (Lufylline ®) in Bronchial Asthma: A Retrospective Survey," Curr. Therap. Res., Vol. 27, No. 6, Section 1, 844 (1980). "Physician's Desk Reference," Ed., Medical Economics Company, Oradell N.J., 1982, pp. 1754.

Poyner, W.J., "Dyphylline Pharmacokinetics Following Two Consecutive Intravenous Infusions in Beagle Dogs," Thesis in the University of Texas at Austin, Texas, 1980. Roth, F.E., Winbury, M.M. and Govier, W.M., Hydroxypropyltheophylline A Pharmacological Comparison with Other Theophylline Preparation," J. Pharmacol. Exp. Therap., 121, 487 (1957). Selvig, K., "Pharmacokinetics of Proxyphylline in Adults After Intravenous and Oral Administration," Eur. J. Clin. Pharmacol., 19, 149 (1981). 160

Selvig, K. and Bjerve, K.S., "Determination of Serum Proxiphylline by High-Pressure Liquid Chromatography," Scand. J. Clin. Lab. Invest. 37, 373 (1977).

Selvig, K. and Bjerve, K.S., "Metabolism of Proxyphylline in Man, Isolation and Identification of Metabolites in Urine," Drug Metab. Dis., Vol. 8, No. 6, 456 (1980). Sharma, P. L. and Sharma, R. M., "Comparative Bioavailability of Sustained-Release and Conventional Tablets of Hydroxyethyltheophylline in man," Int. J. Clin. Pharmacol., Vol. 17, No. 9, 394 (1979).

Simons, F.E.R., Blerman, W., Sprenkle, A.C. and Simons, K.J., "Efficacy of Dyphylline (dihydroxyprophyltheophylline) in Exercise-Induced Bronchospasm," Peds. (suppl), 56, 916 (1975).

Svedmyr, K., Mellstrand, T. and Svedmyr, N., "A Comparison Between Effects of Aminophylline, Proxyphylline and Terbutaline in Asthmatics," Scand. J. Resp. Dis., Suppl. 101, 139 (1977).

Tivenius, C., "Comparison of Drugs for Asthma," Br. Med. J., 2:733 (1971).

Ufkes, J. G. R., Leeuwin, R. S., Ottenhof, M., Zeegers, A. and Zuidema, J., "Efficacy of Theophylline and its N-7-subsituted Derivatives in Experimentally Induced Bronchial Asthma in the Guinea-Pig," Arch. Int. Pharmacodyn., 253, 301 (1981).

"Neo-Biphyllin," Unlisted Drugs, Vol. 28, No. 10, 178 (1976).

"Neo-Biphyllin," Unlisted Drugs, Vol. 31, No. 4, 58 (1979). Zuidema, J. and Merkus, F. W. H. M., "Clinical and Biopharmaceutical Aspects of Theophylline and its Derivatives", Curr. Med. Res. Opin., 6, suppl. 6, 14 (1979). Zuidema, J. and Merkus, F. W. H. M., "Pharmacokinetics and Pharmacodynamics of Diprophylline," Pharm. Weekbl., Sci. Ed., Vol. 3, No. 5, 1320(1981). Zuidema, J., Verhoeven, J. and Merkus, F. W. H. M., "Pharmacokinetics of Etophylline after Intravenous and Oral Administration to Humans," Int. J. Clin. Pharmacol., Vol. 19, No. 7, 310 (1981). APPENDICES 161

APPENDIX

A. Hemolysis of erythrocytes in solutions of xanthine

derivatives.

The method used was the same as that employed by E.R.

Hammarlund and Kaj Pedersen-Bjergaard,1 "Hemolysis of

Erythrocytes in Various Iso-osmotic Solutions." An aqueous solution of saponin,2 100 mg/L was used as the 100% hemolyzing solution for the erythrocytes. Normal saline3 was used as a blank. Fresh venous blood from a rabbit was drawn into a flask containing glass beads. It was immediately defibri- lated by rotating the flask with the beads until the fibrin separated. The blood was poured into a small flask and aerated by rotating gently for 5 mins. The blood was then shaken gently by swirling immediately before each 0.1 ml sample was withdrawn with a Finn pipet. The blood was used immediately.

Compounds studied were aminophylline,4 dyphylline,5 etophylline6and proxyphylline.7 Solutions were freshly prepared. All the compounds were dissolved in distilled water, normal saline or D-5-W8 at three different concentrations except for aminophylline solution which was diluted only with normal saline or D-5-W. 162

10 ml of each solution was added to a centrifuge tube.

Three tubes containing 10 ml of normal saline and three tubes containing 10 ml of saponin served as blank and complete hemolysis respectively. Colorimetric readings were made at the beginning, in the middle and at the end of the experiment for the blank and complete hemolysis samples, 0.1 ml of fresh defibrinated and aerated blood was added to all tubes. The tubes were covered with parafilm9 and inverted several times. The tubes were placed in a water bath at 25°C + 1 for 45 min and were then immediately centrifuged10 for 5 min at 2,000 rpm. The supernatant fluid was decanted and its absorbance determined. The percent of hemolysis was calculated by dividing the absorbance reading for each solution investigated by the reading obtained from the average complete hemolysis samples, times 100%. The experiment was carried out on three different days and the average percent hemolysis are tabulated in Table A.1. 163

Table A.1 Percentage Hemolysis of Erythrocytes in Solutions

Solutions % hemolysis

25 mg/ml aminophylline solution 100

12.5 mg/ml aminophylline in D-5-W 75

6.25 mg/ml aminophylline in D-5-W 55

12.5 mg/ml aminophylline in normal saline 100

6.25 mg/ml aminophylline in normal saline 18

100 mg/ml dyphylline in water 97

50 mg/ml dyphylline in water 96

25 mg/ml dyphylline in water 96

100 mg/ml dyphylline in D-5-W 0

50 mg/ml dyphylline in D-5-W 0

25 mg/ml dyphylline in D-5-W 0

100 mg/ml dyphylline in normal saline 0

50 mg/ml dyphylline in normal saline 0

25 mg/ml dyphylline in normal saline 0

100 mg/ml etophylline in water 97

50 mg/ml etophylline in water 98

25 mg/ml etophylline in water 95

100 mg/ml etophylline in D-5-W 43

50 mg/ml etophylline in D-5-W 0

25 mg/ml etophylline in D-5-W 0 164

Table A.1 (continued)

Solutions % hemolysis

100 mg/ml etophylline in normal saline 0

50 mg/ml etophylline in normal saline 0

25 mg/ml etophylline in normal saline 0

100 mg/ml proxyphylline in water 98

50 mg/ml proxyphylline in water 97

25 mg/ml proxyphylline in water 96

100 mg/ml proxyphylline in D-5-W 0

50 mg/ml proxyphylline in D-5-W 0

25 mg/ml proxyphylline in D-5-W 0

100 mg/ml proxyphylline in normal saline 0

50 mg/ml proxyphylline in normal saline 0

25 mg/ml proxyphylline in normal saline 0

% hemolysis 100 - 100% or more

0 - 0 or less than 1% 165

END NOTES

1. E.R. Hammerlund and Kaj Pedersen-Bjergaard, "Hemolysis

of Erythrocytes in Various Iso-osmotic Solution,"

J. Pharm. Sci., Vol. 50, No. 1, 24 (1961).

2. Saponin Merck, Merck & Co. Inc., New York.

3. Normal saline, 9%, Abbott Laboratories, North

Chicago, IL.

4. Aminophyline injection USP 250 mg (25 mg/ml).

Abbott Laboratories. North Chicago, IL.

5. Dyphylline, Lemmon Company. Sellersville, PA.

6. $-hydroxyethyltheophylline. Sigma Chemical Company.

St. Louis, MO.

7. f3-hydroxypropyltheophylline. Sigma Chemical Company.

St. Louis, MO.

8. D-5-W. Abbott Laboratories. North Chicago, IL.

9. Parafilms. American Can Company. Greenwich, CT.

10. Model TJ-6 Centrifuge. Beckman Instruments. Palo

Alto, CA. 166

A.2 Preparation of the solutions for injection

A.2.1 Aminophylline Aminophylline solutionl was diluted with D-5-W2 to a desired concentration and filtered.3

A.2.2 Dyphylline Dyphylline4 was dissolved in D-5-W to obtain a concentration of 100 mg/ml and filtered.3

A.2.3 Etophylline Etophylline5 was dissolved in D-5-W to obtain a concentration of 50 mg/ml and filtered.3

A.2.4 Proxyphylline Proxyphylline6 was dissolved in D-5-W to obtain a concentration of 100 mg/ml and filtered.4

Dyphylline, etophylline and proxyphylline are diluted with D-5-W to get desired concentration when given as a maintenance dose. 167

Endnotes

1. Aminophylline injection USP 250 mg (25 mg/ml).

Abbott Laboratories. North Chicago, IL.

2. Dextrose 5% in water. Abbott Laboratories.

North Chicago, IL.

3. Aerodisco. Disposable Filter Assembly. Gelman.

4. Dyphylline. Lemmon Company. Sellersville, PA.

5. (3-hydroxyethyltheophylline. Sigma Chemical Company.

St. Louis, MO.

6. $-hydroxypropyltheophylline. Sigma Chemical Company.

St. Louis, MO. 168

A.3 Correction for infusion timea

A* = AaT -0.T 1-e Where A* is an intercept corrected for the infusion

time

A is an intercept obtained from AUTOAN2

a is slope of the line

T is infusion time

These are also time for all intercepts and slopes,

therefore,

B*= W3T 1-e-(37 C* = CYT 1-e-YT

a J.C.K. Loo and S. Riegelman, "Assessment of Pharmacokinetic Constants from Postinfusion Blood Curves

Obtained after I.V. Infusion," J. Pharm. Sci., Vol. 59,

No. 1, (1970). 169

A.4 One compartment open modelb

0.693 ti = kel where kel is slope of the line, determined by

AUTOAN2

X Vd = Co

where X is the amount of drug injected, i.e., dose

Co is plasma drug concentrations immediately after

injection

Cl = Vd kel

X AUC = Vd kel

b Milo Gibaldi and Donald Perrier, "Pharmacokinetics,"

Mercel Dekker, Inc., New York, 1975. pp. 2-17. 170

A.5 Two Compartment Open Modelc

A, a, kel, k12, k21, and V1 are obtained from

AUTOAN2. A* and B* are A and B after correction for infusion

time.

0.693 ti =

A + B AUC = a

X Vd = a AUC

V2 = Vd - V1

Cl = Vd

c Milo Gibaldi and Donald Perrier,"Pharmacokinetics," Mercel Dekker, Inc., New York, 1975. pp. 48-69. 171

A.6 Three Compartment Open Modeld

A, B, C, a, f3, y obtained from AUTOAN2 A*, B* and C* are A, B and C after correction for infusion time.

A* + B* + C* AUC = a R Y

X Va. = A* + B* + C*

X Vd = AUC$

Cl = Vd- 8

0.693 t =

d Milo Gibaldi and Donald Perrier, "Pharmacokinetics,"

Mercel Dekker, Inc., New York, 1975. pp. 89-95