ARTICLE: PDF OnlySybertz Edmund J.; Watkins, Robert W.; Ahn, Ho Sam; Baum, Thomas; Rocca, Paul La; Patrick, James; Leitz, FrederickJournal of Cardiovascular Pharmacology: 1987 - p 105-108 Free Abstract Summary Spirapril (SCH 33844; 7-N-[l(S)-ethoxycarbonyl-3-phenylpropyl]-(S)-alanyl-l.4-dithia-7-azaspiro[4.4]-nonane-8(S)-carboxylic acid) is a new angiotensin-converting enzyme (ACE) inhibitor. SCH 33844 diacid inhibited hydrolysis of hip–his–leu by rabbit lung ACE in a potent (Ki = 0.74 nM), selective, and noncompetitive fashion. SCH 33844 (0.03–1 mg/kg p.o.) produced dose-related inhibition of angiotensin I (AI) pressor responses in conscious rats with a duration of 24 h at the higher dose. SCH 33844 (0.3–30 mg/kg p.o.) reduced blood pressure in a dose-related manner in conscious SHR with a 24-h duration. Antihypertensive activity was enhanced in the presence of hydrochlorothiazide. The drug (1–10 mg/kg p.o.) also lowered blood pressure in conscious hydrochlorothiazide-treated normotensive dogs. In anesthetized dogs, SCH 33844 (1 mg/kg i.v.) reduced blood pressure and total peripheral vascular resistance and slightly increased cardiac output and stroke volume. These results suggest that peripheral vasodilation is the primary mechanism of the antihypertensive action. The metabolic profile of SCH 33844 was evaluated in dogs and rats. The compound was absorbed in a dose-proportional manner and excreted primarily as the diacid form. In contrast to captopril and enalapril, most of the drug (67%) was excreted into the feces following i.v. dosing. Chronic toxicological evaluation in dogs and rats demonstrated that the drug was relatively devoid of toxicity at oral doses as high as 400 and 450 mg/kg/day, respectively. Slight decreases in heart weight (rats) and increases in granularity of the juxtaglomerular apparatus were observed. In conclusion, SCH 33844 is a potent, long acting ACE inhibitor with a low level of toxicity and a metabolic fate that differs from that of enalapril and captopril. Its hemodynamic actions suggest that the compound should be highly effective in the treatment of hypertension and congestive heart failure. Copyright © 1987 Wolters Kluwer Health, Inc. All rights reserved.