Teprotide, a nonapeptide isolated from the venom of a Brazilian pit viper, Bothrops jararaca, was the first angiotensin converting enzyme (ACE) inhibitor to be discovered and tested. It was found to be an effective, non-toxic antihypertensive agent as well as an afterload-reducing agent for patients with congestive heart failure (CHF). The primary activity of teprotide resulted from blockade of the angiotensin I converting enzyme--the pivotal step in the renin-angiotensin-aldosterone system (RAAS), and consequent reductions in angiotensin II levels. There was limited clinical testing for teprotide because of: its scarcity; the need for parenteral administration; and the subsequent discovery and synthesis of captopril, the first orally active angiotensin converting enzyme inhibitor. Captopril is the prototype oral angiotensin converting enzyme inhibitor and has been extensively studied since the initiation of formal studies in 1976. Perhaps one of the most closely researched drugs in modern times, the experience with captopril now includes more than 12,000 patients studied in formalized trials and over 4,000,000 patients treated world-wide by physicians for hypertension and congestive heart failure. Enalapril (MK421) is the first of what appears to be a growing number of analogues which are structurally and pharmacodynamically different from captopril; yet, they possess the same capacity for inhibiting the activity of angiotensin converting enzyme. The side effect profile of enalapril (and presumably future) angiotensin converting enzyme inhibitors appears to be similar to captopril, though clearly more experience is needed with newer agents. The initial use of captopril was troubled by a relatively high incidence of side effects which will form the focus of this discussion. Partially the result of incomplete pharmacokinetic information, captopril was administered in early studies at dosages now recognised to be far in excess of those necessary for drug action. In addition, dosages were given without regard for deficiencies of renal function, now known to be the main excretory route of captopril. The population of those patients studied frequently had chronic, treatment-resistant hypertension, often associated with concomitant end-organ disease (especially renal disease); and many additional factors further complicating the clinical setting, e.g. a relatively high incidence of collagen vascular disease and immunosuppressive treatments.(ABSTRACT TRUNCATED AT 400 WORDS)
