STUDIES WITH NON-STEROIDAL ANTI-INFLAMMATORY DRUGS by Elizabeth Ann Galbraith M.Sc., C.Biol., M.I.Biol. A thesis submitted for the degree of Doctor of Philosophy in the Faculty of Veterinary Medicine of the University of Glasgow Department of Veterinary Pharmacology M ay 1994 ProQuest Number: 11007888 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 11007888 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 4kh! TUT GLASGOW UNIVERSITY ) LIBRARY i To Ian ii TABLE OF CONTENTS Acknowledgements v Declaration vi Summary vii List of tables xi List of figures xv Abbreviations xvii Chapter 1 - General Introduction 1 Chapter 2 - General Material and Methods 29 Chapter 3 - Studies with Flunixin 3.1 Introduction 43 3.2 Experimental Objectives 44 3.3 Materials and Methods 45 3.4 Experiments with Flunixin 48 3.5 Results of Oral Experiments with Flunixin 49 3.6 Results of Intravenous Experiments with Flunixin 53 3.7 Results of Subcutaneous Experiments with Flunixin 55 3.8 Discussion 57 3.9 Tables and Figures 64 Chapter 4 - Studies with Piroxicam 4.1 Introduction 77 4.2 Experimental Objectives 80 4.3 Materials and Methods 80 4.4 Experiments with Piroxicam 83 4.5 Results of Experiments with Piroxicam 84 4.6 Discussion 88 4.7 Tables and Figures 94 Chapter 5 - Studies with Cinchophen 5.1 Introduction 105 5.2 Experimental Objectives 106 5.3 Materials and Methods 107 5.4 Experiments with Cinchophen 110 5.5 Results of Experiments with Cinchophen 111 5.6 Discussion 117 5.7 Tables and Figures 122 Chapter 6 - Studies with Tolfenamic Acid 6.1 Introduction 132 6.2 Experimental Objectives 135 6.3 Materials and Methods 135 6.4 Experiments with Tolfenamic Acid 138 6.5 Results of Experiments with Tolfenamic Acid 140 6 .6 Discussion 144 6.7 Tables and Figures 149 Chapter 7 - Protein Binding of Flunixin Meglumine and Meclofenamic Acid 7.1 Introduction 161 7.2 Experimental Objectives 166 7.3 Materials and Methods 166 7.4 Results of Dialysis Experiments with Flunixin and Meclofenamic Acid 170 7.5 Discussion 170 7.6 Tables and Figures 174 Chapter 8 - Studies on the Inhibition of Ex Vivo Production Serum Thromboxane by Non- steroidal Anti-inflammatory Drugs. iv 8.1 Introduction 181 8.2 Experimental Objectives 184 8.3 Materials and Methods 185 8.4 Results 187 8.5 Discussion 190 8 .6 Tables and Figures 195 Chapter 9 - General Discussion 209 Appendix 1 - Extraction Recoveries of Drugs 221 Appendix 2 - Flunixin Oral Administration Tables 226 Appendix 3 - Flunixin Intravenous Administration Tables 233 Appendix 4 - Flunixin Subcutaneous Administration Tables 239 Appendix 5 - Piroxicam Intravenous Administration Tables 245 Appendix 6 - Piroxicam Oral Administration Tables 251 Appendix 7 - Cinchophen Intravenous Administration Tables 257 Appendix 8 - Cinchophen Oral Administration Tables 263 Appendix 9 - Tolfenamic Acid Intravenous Administration Tables 269 Appendix 10 - Tolfenamic Acid Subcutaneous Administration Tables 275 Appendix 11 - Protein Binding Tables 281 Appendix 12 - In vitro Inhibition of Serum Thromboxane Tables 284 References 294 V ACKNOWLEDGEMENTS I would like to express my gratitude to the late Professor James A. Bogan who encouraged me to embark upon this project and without who’s faith in my ability I would not have had the confidence to take the first steps. I would also like to thank Dr Q.A. McKellar for being prepared to take over the role of supervisor and allowing my work to continue. For technical assistance and support, I would like to thank my fellow technical staff in the department of Veterinary Pharmacology - Mr P. Baxter, Mr I McKinnon, Mrs M Michael, Mr R McCormack and Mrs H. Brown. I am also indebted to the staff of the Haematology Laboratory of the Veterinary Pathology Department - Mr R Barron and Mr K Williamson, who performed the blood platelet counts, and Mr A Bradley and staff who assisted with other practical aspects of the work. Finally, I would like to thank Dr L. Horspool and Dr E. Welsh for their enthusiastic support I can only hope I taught them as much as they taught me. DECLARATION The estimation of serum thromboxane inhibition after oral administration of flunixin meglumine to dogs was carried out by Professor Peter Lees of London University. Platelet numbers were estimated by the staff of the Department of Veterinary Pathology at he University of Glasgow Veterinary School. Otherwise the contents of this thesis are the work of the author. The thesis has not been submitted to any University for the award of a degree. The following publications are base on the work contained in this thesis: McKellar, Q.A., Galbraith, E.A., Bogan, J.A., Russell, C.S., Hooke, R.E. and Lees, P. Flunixin pharmacokinetics and serum thromboxane inhibition in the dog. Veterinary Record (1989), 124.651-654 Galbraith, E.A. and McKellar, Q.A. Pharmacokinetics and pharmacodynamics of piroxicam in dogs. Veterinary Record (1991), 128.561-565 McKellar, Q.A., Pearson, T., Galbraith, E.A., Boyle, J. and Bell, G. Kinetics and clinical efficacy of cinchophen and prednisolone combination in the dog. Journal of Small Animal Practice (1991), 22, 53-58 McKellar, Q.A., Galbraith, E.A. and Simmons, R.D. Pharmacokinetics and serum thromboxane inhibition of two non-steroidal anti-inflammatory drugs when administered to dogs by the intravenous and subcutaneous routes. Journal of Small Animal Practice (1991), 22.335-340 SUMMARY The pharmacokinetics and serum thromboxane inhibition of four non-steroidal anti­ inflammatory drugs (NSADDs) were determined after administration to dogs by the intravenous, subcutaneous and oral routes. Flunixin meglumine was first administered at three oral dose rates, 0.55, 1.10 and 1.65 mg/kg, to determine a likely suitable dose rate by this route. At each dose rate the mean maximum plasma concentration of drug (Cmax ) occurred between 1 and 2 hours. After 0.55, 1.10 and 1.65 mg/kg the Cmax increased approximately in relation to the dose rate and values were 2.77 ± 0.63,5.03 ± 0.99 and 8.17 ± 2.02 pg/ml respectively. The mean area under the plasma concentration versus time curve (AUC) was 9.01,14.62 and 25.98 |ig/ml.h after 0.55,1.10 and 1.65 mg/kg. Maximum mean inhibition of serum thromboxane (TxB 2) was 91.47, 98.84 and 97.31 % and occurred between 1 and 2 hours. The area under the TxB 2 inhibition versus time curve was not linearly related to dose rate and was determined to be 5238, 5952 and 6169 %.h respectively for 0.55, 1.10 and 1.65 mg/kg dose rates . On the basis of the findings from the oral experiments the 1.10 mg/kg dose rate was selected for study after intravenous and subcutaneous administration. The decline in plasma concentration of flunixin meglumine after intravenous administration was best described by a bi-exponential equation. The mean half life of elimination (t V 2B) in dogs was 2.97 hours and the mean volume of distribution at steady state (Vdss) was 189.23 ± 46.70 ml/kg. The AUC from observed values after administration at a dose rate of 1.10 mg/kg was 20.47 ± 2.60 pg/ml.h. Determination of the AUC after intravenous administration allowed calculation of the bioavailability (F) after oral administration. After normalisation for dose rate the bioavailability after oral administration of flunixin to dogs was 74.8,60.66 and 69.8 %.for the 0.55,1.10 and 1.65 mg/kg dose rates respectively, thus indicating that absorption was approximately linearly related to dose rate administered. The maximum mean inhibition of serum TxB 2 after intravenous administration was 99.87 % (0.5 hours), and the area under the TxB 2 inhibition versus time curve was 2148 %.h, approximately 36 % of the area under the TxB 2 inhibition versus time curve obtained after the equivalent dose rate administered by the oral route. After subcutaneous administration at a dose rate of 1.10 mg/kg the Cmax of flunixin in plasma was 6.36 |ig/ml, and this occurred at 0.92 hours. Bioavailability was excellent after subcutaneous administration, the AUC being 26.30 ± 4.73 |ig/ml.h (F=101.09 %). viii The maximum mean inhibition of TxB 2 after subcutaneous administration was approximately equal to that after intravenous administration (99.73 % at 1 hour), as was the area under the TxB 2 inhibition versus time curve. This AUC was also approximately half of the AUC produced by the oral administration of the same dose rate. No adverse reactions were observed after administration of flunixin meglumine to dogs. After administration at a dose rate of 0.3 mg/kg by the intravenous route to dogs, the decline in plasma concentration of piroxicam was best described by a single exponential equation. The fit of the mathematically modelled best fit curve was very poor for all animals. The tV 2^ was calculated to be 40.16 hours and the Vdss calculated from observed data was 178.37 ml/kg. The observed AUC of piroxicam after intravenous administration was 47.39 |ig/ml.h.