Objective: Two different conventional release enalapril maleate tablet formulations were evaluated for their relative bioavailability (Eupressin tablets 10 mg, Biosintetica as the test formulation vs Renitec tablets 10 mg Merck Sharp and Dhome, as the reference formulation). A single 20 mg oral dose of each preparation was administered to 18 healthy male adult volunteers and their bioequivalence was assessed by comparing the serum enalaprilat and total enalapril (enalaprilat plus enalapril maleate) concentration-time curves. Angiotensin converting enzyme (ACE) activity was also quantified in each serum sample. Results: The pharmacokinetic parameters obtained for each formulation were the area under the time-concentration curve from 0 to 24 h (AUC[0-24]), maximum concentration C(max) and the time at which it occurred (t(max)). When serum enalaprilat concentration-time curves were employed to assess bioequivalence, the formulations were bioequivalent in the extent but not in the rate of absorption. However, no difference in either the extent or the rate of absorption were observed when serum total enalapril vs time curves were analysed. ACE activity-time curves were similar for both formulations and showed that ACE was 90% inhibited 3-5 h after enalapril administration, and till approximately 50% after 24 h. At that time, circulating enalaprilat and total enalapril levels were less than the tenth of C(max). 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