Pectoris with Erythrityl Tetranitrate, Glyceryl Trinitrate, Isosorbide

Home , Isosorbide dinitrate, Propatylnitrate

AN ABSTRACT OF THE THESIS OF

ARTHUR ALLAN STIPE for the Master of Science (Name of student) (Degree) in Pharmacology and Toxicology presented on --)9q0,0:7J91 (Major) (De) Title: PROPHYLACTIC THERAPY OF ANGINA PECTORIS WITH

ORGANIC NITRATES: RELATIONSHIP OF DRUG EFFICACY

AND CLINICAL EXPERIMENTAL DESIGN Redacted for Privacy Abstract approved: Gregory B. Fink

The objective of this study was to examine the published clinical literature on the prophylactic therapy of angina pectoris with the organic nitrates in order to determine the relationship between experimental design and the conclusion of efficacy reported by the investigator. A search for articles reporting original clinical investigations on immediate and long term prophylactiC therapy of angina pectoris with erythrityl tetranitrate, glyceryl trinitrate, isosorbide dinitrate or pentaerythritol tetranitrate yielded 59 articles that were published in the period of 1952 to 1972. The design elements of an adequate and well controlled clinical trial include a method of minimizing bias on the part of the observer and patient (blinding procedures), appropriate control procedures, statistical analysis and appropriate treatment allocation procedures. The proportion of articles concluding effective therapy with the organic nitrates was significantly greater among the investigations that failed to report any of these generally accepted design elements. Clinical investigations finding the organic nitrates as effective prophylactic agents outnumbered the investigations reporting ineffective therapy by almost three to one. Among the investigations that included the generally accepted design elements of an adequate and well controlled clinical trial, the reports of ineffective prophylactic therapy outnumbered the reports of effective therapy by three to two. Although simply including these design elements will not necessarily validate the conclusions reached by the investigator, their importance is dramatically illustrated in the present study.Because of these demonstrated relationships, any consideration of efficacy of the organic nitrates in the prophylactic therapy of angina pectoris must be weighed against considerations of experimental design in a given clinical trial. Prophylactic Therapy of Angina Pectoris with Organic Nitrates: Relationship of Drug Efficacy and Clinical Experimental Design

by Arthur Allan Stipe

A THESIS submitted to Oregon State University

in partial fulfillment of the requirements for the degree of Master of Science June 1973 APPROVED:

Redacted for Privacy

Professor of Pharmacology in charge of major Redacted for Privacy

Chairman of Pharmacology

Redacted for Privacy

Dean of Graduate School

Date thesis is presented --YY),,,64 1973 Typed by Opal Grossnicklaus for Arthur Allan Stipe TABLE OF CONTENTS Page

INTRODUCTION 1

MATERIALS AND METHODS 3

RESULTS AND DISCUSSION 5

SUMMARY 1 2

BIBLIOGRAPHY 13 LIST OF TABLES

Table Page

1. Drugs studied and conclusion of efficacy reported in 59 clinical trials published from 1952 to 1972. 6

2. Relationship between elements of experimental design and conclusion of efficacy in clinical investigations of antianginal therapy with the organic nitrates. 8

3. Summary of the relationship between experimental design and conclusion of efficacy reported in clinical investigations of antianginal therapy with the organic nitrates. 11 PROPHYLACTIC THERAPY OF ANGINA PECTORIS WITH ORGANIC NITRATES: RELATIONSHIP OF DRUG EFFICACY AND CLINICAL EXPERIMENTAL DESIGN

INTRODUCTION

The organic nitrates are used to achieve three distinct pallia- tive therapeutic goals in angina pectoris: (1) termination of an acute attack; (2) prevention of attacks by administration of medication shortly before an expected attack (immediate prophylaxis); and (3) prevention of attacks that occur in the day to day life of the patient with angina (long term prophylaxis).Traditionally amyl nitrate and nitroglycerin have been used to terminate the acute attack; however, the efficacy of the organic nitrates in preventing attacks remains undecided. Guidelines for an adequate and well controlled clinical investigation have been provided to underwrite the accuracy of clinical measurements (1).These guidelines suggest that certain elements of experimental design can serve as a means of reducing bias or systematic errors that occur in clinical experiments.Although these elements of experimental design are not appropriate in all clinical investigations, their importance in drug efficacy research has been recognized by the Food and Drug Administration in defining criteria for an adequate and well controlled clinical investigation (1). 2 The purpose of this paper is to examine published clinical investigations to determine the relationship between the generally recognized elements of experimental design and the stated conclusion of efficacy of the organic nitrates in immediate and long term prophylactic therapy of angina pectoris. 3

MATERIALS AND METHODS

Articles reporting clinical studies on prophylactic therapy of angina pectoris with erythrityl tetranitrate (ETN), glyceryl trinitrate (NTG), isosorbide dinitrate (ISDN) and pentaerythritol tetranitrate (PETN) were the subject of a literature search for the period 1952 to 1972.Other organic nitrates provided an insignificant share of the 1971 prescription market for "coronary vasodilators" (2) and were not included. Only articles reporting original clinical investigations were considered for evaluation.These "study articles" (3 -61) were abstracted with a general format describing the source of the article, drugs evaluated, patient characteristics, investigational design and the investigator's stated conclusion of effectiveness of the drugs studied.The abstracts were divided into three categories based on whether the organic nitrate was investigated for its use in immediate prophylaxis, long term prophylaxis, or both immediate and long term prophylaxis. When the investigator concluded that at least one of the organic nitrates was effective as a prophylactic agent, the article was classi- fied as effective.The classification of ineffective was assigned when none of the organic nitrates investigated were effective.Contingency tables were constructed on the basis of these classifications, and 4 the exact probabilities given in the tables were calculated under the hypothesis of independence (62). 5 RESULTS AND DISCUSSION

The search for original clinical investigations on the efficacy of the organic nitrates currently used yielded 59 articles for study. Forty three of these study articles reported the drugs to be effective and 16 reported them to be ineffective.Long term prophylaxis was considered in 36 study articles with 23 reporting effective and 13 reporting ineffective therapy.Immediate prophylaxis was considered in 30 study articles with 24 reporting effective and six reporting ineffective therapy. The frequencies with which the drugs appeared and the conclusions of efficacy reached in the study articles are listed in Table 1. Erythrityl tetranitrate (ETN) was not considered in the analysis of the clinical literature on long term prophylaxis because the drug appeared in only one investigation.Analysis of the data in the table revealed no significant differences in the proportion of articles reporting effective to articles reporting ineffective therapy between the individual drugs. Although the majority of the investigators found the drugs to be effective, a considerable number found them to be ineffective. Therefore, the experimental design of each clinical investigation was examined to determine if the elements of experimentaldesign were related to the differences in conclusions reached by theinves- tigators. 6

Table 1.Drugs studied and conclusion of efficacy reported in 59 clinical trials published from 1952 to 1972. Drugs Number of Articles Studied Effective Ineffective All Study Articles

PETN 12 9 ISDN 22 5 NTG 14 3 ETN 6 0 Long Term Prophylaxis PETN 7 7 ISDN 13 4

NTG 4 3 Immediate Prophylaxis PETN 8 2 ISDN 10 4 NTG 11 0 ETN 6 0

PETN = pentaerythritol tetranitrate; ISDN = isosorbide dinitrate; NTG = glyceryl trinitrate; ETN = erythrityl tetr anitrate. 7 The design elements of an adequate and well controlled clinical trial include a method of minimizing bias on the part of the observer and patient (blinding procedures), appropriate control procedures, statistical analysis and appropriate treatment allocation procedures. The relationship between these elements of design and the conclusion of efficacy in the study articles is shown in Table 2. A majority of the study articles reported either single or double blinding procedures as a means of reducing bias error introduced by observers or patients; however, a considerable number of the articles did not report any attempt to conceal the identity of the treatment procedures.Problems encountered with blinding procedures include patient recognition of the active drug by its characteristic side effects or hemodynamic actions (13, 17, 19) and difficulty in dosage indi- vidualization within the double blind framework (63).It should be noted that investigations which did not report blinding procedures invariably found the drugs to be effective. Control procedures reported in the articles included no treatment, active treatment, historical and placebo controls.Placebo controls should be considered the only appropriate control procedure for investigation of long term or immediate prophylaxis. An experi- ment with no treatment controls assumes, and indeed requires, negligible placebo responsiveness; however, Beecher (64) has sug- gested that as many as 35% of patients may be expected to respond 8

Table 2.Relationship between elements of experimental design and conclusion of efficacy in clinical investigations of anti anginal therapy with the organic nitrates.

Design Number of Articles Elements Effective Ineffective

All Study Articles

Blinding 21 16 No blinding 22 0 P < . 01 Controls 35 16 No controls 8 0 P =065 Statistics 14 12 No statistics 29 4 P < . 01 Long Term Prophylaxis

Blinding 13 13 No blinding 10 0 P < . 01 Placebo 15 13 No placebo 8 0 P < . 02 S tatistics 7 9 No statistics 16 4 P < . 03 Random 9 13 Nonrandom 9 0 P <,. 01 Crossover 12 13 No crossover 6 0 P < . 03 Immediate Prophylaxis Blinding 11 6 No blinding 13 0 P < .02 Placebo 13 6 No placebo 11 0 P < 02 Statistics 6 6 No statistics 18 0 P < . 05 Random 7 Nonrandom 16 0 P < . 01 Crossover 17 6 No crossover 6 0 P= . 213 P r.= probability that the proportion of effective to ineffective articles is the same between the classifications. 9 favorably to placebo therapy.The value of active treatment controls is questionable because there is no widely accepted standard treatment in the prophylactic therapy of angina pectoris.Historical controls are inadequate because there is great variability between patients with angina and the drugs lack dramatic effectiveness.Again, it can be seen that investigations which did not report appropriate controls consistently found the drugs effective. Statistical analysis of the data was indicated in less than one half of the study articles.Problems in selecting the statistical method which is appropriate for the analysis of clinical data have been discussed by Mainland (65) and Feinstein (66).The study articles were not evaluated to determine if the method was appropriate.Nevertheless, Table 2 indicates that application of any statistical analysis diminished the proportion of studies finding the drugs effective. Appropriate treatment allocation procedures include random allocation and crossover of treatments. Random allocation may be required because of the systematic error introduced by carry over effects from an effective previous therapy (67) and by warm up effects on repeated exercise tolerance testing (34, 68).Furthermore, crossover of treatments may be required because of the great variability in the baseline of response between patients with angina.Investiga- tions which did not include either of these design elements found the 10 drugs effective without exception. A compilation of the elements of experimental design as they occurred in the study articles is given in Table 3.Clinical investigations finding the organic nitrates as effective prophylactic agents in the therapy of angina pectoris outnumbered the investigations reporting ineffective therapy by almost three to one. Among the investigations that included the generally accepted design elements to reduce experimental error, the reports of ineffective prophylactic therapy outnumbered the reports of effective therapy by three to two. From these observations, it can be seen that there is a definite relationship between experimental design and the conclusion of efficacy of the organic nitrates in the prophylactic therapy of angina pectoris.There was a significantly greater proportion of articles reporting effective therapy with the drugs among the investigations that did not include the generally accepted elements of experimental design which serve as a means of reducing bias or systematic error. Although simply including these design elements will not necessarily validate the conclusions reached by the investigator, their importance is dramatically illustrated in the present report.Because of these demonstrated relationships, any consideration of efficacy of the organic nitrates in the prophylactic therapy of angina pectoris must be weighed against considerations of experimental design in a given clinical trial. 11

Table 3.Summary of the relationship between experimental design and conclusion of efficacy reported in clinical investigations of antianginal therapy with the organic nitrates.

Articles Number of Articles Including Effective Ineffective Total

All Study Articles Study articles 43 16 59

BLD 21 16 37

BLD, CON 19 16 35

BLD, CON, STAT 10 12 22

BLD, CON, STAT, RDM 8 12 20

Long Term Prophylaxis

Study articles 23 13 36

BLD 13 13 26

BLD, PCB 12 12 24

BLD, PCB, STAT 6 9 15

BLD, PCB, STAT, RDM 6 9 15

Immediate Prophylaxis

Study articles 24 6 30

BLD 11 6 17

BLD, PCB 10 6 16

BLD, PCB, STAT 4 6 10

BLD, PCB, STAT, RDM 2 6 8

BLD = blinding; CON = controls; STAT = statistical analysis; RDM = random allocation of treatments; PCB = placebo. 12

SUMMARY

Fifty nine clinical investigations published from 1952 to 1972 on the prophylactic therapy of angina pectoris with the organic nitrates were examined to determine if the generally accepted elements of experimental design were related to the reported conclusion of efficacy of these drugs.These generally accepted elements of experimental design serve as a means of reducing bias or systematic experimental errors.The relationship was highly significant in that inclusion of any of the design elements markedly decreased the proportion of investigations reporting the drugs to be effective. 13

BIBLIOGRAPHY

1. United States: Federal Register 35 (90):7251, May 8, 1970.

2. Gosselin, R. A. and Company: National Prescription Audit. p. 166, Dec. 1971.

3. Abrahamsen, A. M., Kiil, F.: Exercise Performance and Electrocardiographic Changes as Indicesof Effect of Long- acting Nitrates in Angina Pectoris.Br. Med. J. 1:456 (1966).

4. Adolfsson, I., Areskog, N. H. ,Rasmuson, T.: Effects of Alprenoloi and Sorbidinitrate During Exercise in Patients with Coronary Insufficiency.Eur. J.Clin. Pharmacol. 3(2):68 (1971).

5. Altman, George E., Riseman, Joseph E. F., Koretsky S.: Sublingual Erythrol Tetranitrate in the Treatment of Angina Pectoris.Effect of Varying the Dose and Rate of Administra- tion.Am. J. Med. Sci. 240:66 (1960).

6. Aronow, Wilbert S., Chesluk, Herman M.: Sublingual Iso- sorbide Dinitrate Therapy Versus Sublingual Placebo in Angina Pectoris.Circulation 41:869 °(1970).

7. Aronow, Wilbert S., Kaplan, Marvin A.: Evaluation of Propranolol and of Isosorbide Dinitrate in Angina Pectoris. Curr. Ther. Res. 11:80 (1969).

8. Aubert, A., Nyberg, G. ,Slaastad, R., Tjeldflaat, L.: Prophylactic Treatment of Angina Pectoris. A Double-blind Cross-over Comparison of Alprenolol and Pentanitrol.Br. Med. J. 1:203 (19 70).

9. Battock, Dennis J., Alvares, Hector, Chidsey, Charles A. Effects of Propranolol and Isosorbide Dinitrate on Exercise Performance and Adrenergic Activity in Patients with Angina Pectoris.Circulation 39:157 (1969).

10. Bellet, Samuel, Muller, Otto F. ,Herring, Allen B., LaVan, Donald W.: Effect of Erythrityl Tetranitrate on the Electro- cardiogram as Recorded During Exercise by Radioelectrocardi- ography. Am. J. Cardiol. 11:600 (1963). 14

11. Berry, John W., Carney, Ross, Lankford, Hal:Clinical Experiences with Isosorbide Dinitrate (ISORDIL).Angiology 12:254 (1961).

12. Bidwai, P. S., Khattri, H. N., Vohra, R. K., Berry, J. N.: Double Blind Controlled Clinical Trial of a Long Acting Coro- nary Vasodilator Isosorbide Dinitrate (SORBITRATE).J. Assoc. Physicians India 16:853 (1968).

13. Blinder, Samuel: The Evaluation of Controlled-Released Nitroglycerin Tablets (NITRONG) in the Treatment of Angina Pectoris.Curr, Ther. Res. 7:769 (1965).

14. Bunn, William H.Chremos, A. N.: Clinical Evaluation of Sublingual Nitrates.Onset and Duration of Action of Nitro- glycerin and Isosorbide Dinitrate.Angiology 14:48 (1963).

15. Cole, Ralph E., Goldberg, Ronald I.:Timed-Release Penta- erythritol Tetranitrate and Placebo in the Management of Angina Pectoris.Curr. Ther, Res. 9:551 (1967).

16. Cole, Seymour L. ,Kaye, Harry, Griffith, George C.: Assay of Antianginal Agents - The Rapport Period. JAMA 168:275 (1958).

17. Cole, Seymour L., Kaye, Harry, Griffith, George C.: Assay of Anti-Anginal Agents I.A Curve Analysis with Multiple Control Periods.Circulation 15:405 (1957).

18. Dagenais, Giles R. ,Mason, Robert E. ,Friesienger, Gottlieb C., Wender, Charles, Ross, Richard S.: Exercise Tolerance in Patients with Angina Pectoris: Daily Variation and Effect of Pentaerythritol Tetranitrate.Johns Hopkins Med. J. 125:301 (1969).

19. Dagenais, Giles R., Pitt, Bertram, Ross, Richard S.: Exer- cise Tolerance in Patients with Angina Pectoris.Daily Vari- ation and Effects of Erythrityl Tetranitrate, Propranolol and Alprenoloi. Am. J. Cardiol. 28:10 (1971).

20. Datey, K. K. ,Dalvi, C. P.: Isosorbide Di-nitrate (SORBITRATE) - A New Antianginal Drug.J. Assoc. Physi- cians India 12:635 (1964). 15

21. Evangelista, Italo:Sustained Action Glyceryl Trinitrate in the Treatment of Angina Pectoris.J. Lancet 88:111 (1968).

22. Evans, D. W., Domenet, J. G.: A Controlled Trial of Long- Acting Glyceryl Trinitrate for the Prevention of Angina Pec- toris.Postgrad. Med. J. 40:351 (1964).

23. Fremont, Rudolph E.: Controlled Observations of Clinical Efficacy of Isosorbide Dinitrate.Geriatrics 16:520 (1961).

24. Goldbarg, Alberto N.,Moran, John F.Butterfield, Thomas K., Nemickas, Rimgaudas, Bermudez, Gustavo A.: Therapy of Angina Pectoris with Propanolol and Long-Acting Nitrates. Circulation 40:847 (1969).

25. Goldstein, Robert E.,Rosing, Douglas R., Redwood, David R., Beiser, G. David, Epstein, Steven E.:Clinical and Circula- tory Effects of Isosorbide Dinitrate.Comparison with Nitro- glycerin.Circulation 43:629 (1971).

26. Gorman, Patrick A., Evans, John M.: The Effects of Chewable Isosorbide Dinitrate in Coronary Insufficiency. A Report on Exercise Electrocardiograms in 13 Patients.Med. Ann. D. C. 40:235 (1971).

27. Gulati, R. B., Mutalik, G. S.: A Sequential Trial of Isosorbide Dinitrate (' SORBITRATE') in Angina Pectoris.Indian Practi- tioner 19:245 (1966).

28. Hirshleifer, Irving.: A Pharmacodynamic Approach to the Evaluation of Nitrates in the Treatment of Angina Pectoris. Am. J. Cardiol. 5:66 (1960).

29. Jacobs, L. J.:Sorbide Nitrate in the Management of Angina Pectoris in General Practice.Practitioner 197:225 (1966).

30. Jaffe, G. V., McGuiness, B. W.: Clinical Trial of Sorbide Nitrate A Long-Acting Coronary Artery Dilator.Practitioner 190:241 (1963).

31. Joseph, Lester G.,Mancini, A.: Isosorbide Dinitrate in Angina Pectoris.Angiology 1 2:264 (1961). 16

32. Kalmanson, George M., Drenick, Ernst J., Binder, Maxwell J., Rosove, Leon: Pentaerythritol Tetranitrate in the Treatment of Angina Pectoris.Arch. Intern. Med. 95:819 (1955).

33. Kini, P. M., Chandrasekharan, K. G.Pai, K. N.: Iso- sorbide Di-Nitrate (SORBITRATE) in the Treatment of Angina Pectoris.J. Assoc. Physicians India 14:709 (1966).

34. MacAlpin, Rex N., Kattus, Albert A., Winfield, Mark E.: The Effect of a beta-Adrenergic-Blocking Agent (Nethalide) and Nitroglycerin on Exercise Tolerance in Angina Pectoris.Cir- culation 31:869 (1965).

35. MacKay, Eaton M.: Isosorbide Dinitrate in Angina Pectoris. An Evaluation of Sublingual and Oral Administration.Western Med. 2:338 (1961).

36. Neumann, Marcel, Luisada, Aldo A.: Effect of Rapid- and Slow-Acting "Coronary" Drugs on Precordial Pain of the Aged. Am. J. Med. Sci. 247:1 56 (1964).

37. Oram, Samuel, Sowton, Edgar: Failure of Propatylnitrate and Pentaerythritol Tetranitrate to Prevent Attacks of Angina Pec- toris.Br. Med. J.2:1 745 (1961). 38. Parry, E. H. 0., Wells, P. G.:Clinical Trial of Two Coronary Vasodilator Drugs.Br. Med. J1:26 (1960). 39. Pilkington, T. R. E., Purves, M. J.:Long-acting Glyceryl Trinitrate in Angina Pectoris of Out-patients.Br. Med. J. 1:38 (1960).

40. Poltz, Milton: The Treatment of Angina Pectoris with a New Prolonged Action Pentaerythritol Tetranitrate.Am. J. Med. Sci. 239:194 (1960). 41. Riseman, Joseph E. F.Altman, George E., Koretsky, Sidney: Nitroglycerin and Other Nitrates in the Treatment of Angina Pectoris.Comparison of Six Preparations and Four Routes of Administration.Circulation 1 7:22 (1958).

42. Riseman, Joseph E. F., Koretsky, Sidney, Altman, George E.: Stereo-Isomeric Nitrates in the Treatment of Angina Pectoris. Am. J. Cardiol. 15:220 (1965). 17

43. Ruskin, Arthur: Effects of Erythrol Tetranitrate and Amotriphene on Exercise Tolerance Tests in Angina Pec- toris.Circulation 23:681 (1961). 44. Russek, Henry I.:The Therapeutic Role of Coronary Vaso- dilators: Glyceryl Trinitrate, Isosorbide Dinitrate, and Pentaerythritol Tetranitrate.Am. J. Med. Sci. 252:9 ( 1966).

45. Russek, Henry Propranolol and Isosorbide Dinitrate Synergism in Angina Pectoris. Am. J. Med. Sci. 254:406 (1967).

46. Russek, Henry I.: New Dimension in Angina Pectoris Therapy. Geriatrics 24:81 (1969).

47. Russek, Henry I., Howard, J. Campbell: Glyceryl Trinitrate in Angina Pectoris. JAMA 189:108 (1964).

48. Russek, Henry I.,Urbach, Karl F.,Doerner, Alexander A., Zohman, Burton L.: Choice of a Coronary Vasodilator Drug in Clinical Practice. JAMA 1 53:207 (1953).

49. Russek, Henry I., Zohman, Burton L., Dorset, Virgil J.: Objective Evaluation of Coronary Vasodilator Drugs. Am. J. Med. Sci. 229:46 (1955).

50. Russek, Henry I., Zohman, Burton L., Drumm, Alice E., Weingarten, William, Dorset, Virgil J.: Long-Acting Coro- nary Vasodilator Drugs: Metamine, Paveril, Nitroglyn and Peritrate.Circulation 1 2:169 (1955).

51. Sandler, G., Ilahi, M. A., Lawson, C. W.: Glyceryl Tri- nitrate in Angina Pectoris.Lancet 1:1130 (1963).

52. Sapienza, Peter, L.: Treatment of Angina Pectoris: A Double- Blind Study.Clin. Med. 75:30 (1968).

53. Semler, Herbert J.: The Use of Isosorbide Dinitrate in Status Anginosis.Curr. Ther. Res. 12:789 (1970)

54. Semler, Herbert J., Orvis, Harold H.: Angina Prophylaxis by Chewable Isosorbide Dinitrate.Curr. Ther. Res. 13:523 (1971). 18

55. Sepaha, G. C., Jain, S. R., Chatterji, A. N., Chandrakar, M. P.: Isosorbide Di-Nitrate in Angina Pectoris. A Double- blind-study of 50 Cases.Indian Heart J. 22:17 (1970).

56. Shapiro, Shepard: Angina Pectoris.Treatment with Isosorbide Dinitrate.Angiology 1 2:53 (1961).

57. Smith, Arthur L.: Treatment of Angina Pectoris with a New Coronary Vasodilator, Isosorbide Dinitrate Sublingual (ISOSORBIDE SUBLORAL). Angiology 13:425 (1962).

58. Spier,Lester C.: Uniform Release Nitroglycerin for Pro- phylactic Use.Clin. Med. 76:23 (1969).

59. Talley, Robert W. ,Beard, Owen W., Doherty, James E.: Use of Pentaerythritol Tetranitrate (PERITRATE) in Treatment of Angina Pectoris.Am. Heart J. 44:866 (1952).

60. Weitzman, David: Penta-erythritol Tetranitrate in Treatment of Angina.Br. Med. J. 2:1409 (1953).

61. Winsor, Travis, Scott, Charles C.: Further Observations of Cardiovascular Effects of Pentaerythritol Tetranitrate in Animals andMan. Am. Heart J. 49:414 (1955).

62. Goldstein, Avram: Biostatistics: An Introductory Text.The MacMillan Company, New York, 1964, p. 110.

63. Datey, K. K.: Anti Anginal Drugs,Their Evaluation by Double Blind Trial.Angiology 21:520 (19 70).

64. Beecher, Henry K.: Appraisal of Drugs Intended to Alter Sub- jective Responses, Symptoms. JAMA 158:399 (1955).

65. Mainland, Donald:Statistical Ward Rounds-1. Clin. Pharmacol. Ther. 8:139 (1967).

66. Feinstein, Alvan R. :Clinical Biostatistics.XII On Exorcis- ing the Ghost of Gauss and the Curse of Kelvin.Clin. Pharm- acol. Ther. 12:1003 (19 71).

67. Batterman, Robert C.: Placebo Responsiveness - Influence of Previous Therapy.Curr. Ther. Res. 10:136 (1968). 19

68. Wayne, E. J., Graybiel, Ashton: Observations on the Effect of Food, Gastric Distension, External Temperature, and Re- peated Exercise on Angina of Effort, with a Note on Angina Sine Do lore.Clin. Med. 1:287 (1934).