Spirapril. A preliminary review of its pharmacology and therapeutic efficacy in the treatment of hypertension.

Spirapril is a non-sulfhydryl angiotensin converting enzyme (ACE) inhibitor prodrug which is converted to the active metabolite spiraprilat following oral administration, and which has been evaluated primarily for the treatment of hypertension. In dose-finding studies of patients with mild to severe hypertension, spirapril > or = 6 mg once daily produced reductions in blood pressure of approximately 10 to 18 mm Hg (systolic) and 7 to 13 mm Hg (diastolic) [24-hour postdose trough readings at the end of the treatment period]. Blood pressure normalisation (trough diastolic blood pressure < or = 90 mm Hg) had occurred in 29 to 50% of patients at the end of these investigations. The dose-response curve for spirapril appears to be flat for doses of 6 to 24 mg once daily. Comparisons with other ACE inhibitors are limited in number, and further studies are required before the relative antihypertensive efficacy of spirapril can be fully evaluated. However, in single, well controlled clinical trials, spirapril produced similar reductions in blood pressure to those seen with enalapril or captopril. When given as monotherapy or in combination with hydrochlorothiazide, spirapril may offer potential advantages over the calcium antagonist nitrendipine. Spirapril is generally well tolerated and produces an adverse event profile similar to that of other ACE inhibitors. Data from small studies suggest that spirapril can be used without dosage adjustment in patients with renal impairment, as a consequence of its dual renal and hepatic clearance mechanisms. This is in contrast to most ACE inhibitors, which are eliminated by a predominantly renal mechanism that results in accumulation of the active metabolite when renal function is impaired. However, the utility of spirapril in this patient group has yet to be fully determined because of conflicting data regarding its effects on renal function. Thus, spirapril is an effective antihypertensive agent which is well tolerated. Further comparative trials are needed to fully determine its efficacy with respect to other ACE inhibitors, and a better understanding of its effects on renal function will clarify its role in hypertensive patients with renal failure.