Relative bioavailability study of 20-mg enalapril tablets in healthy male volunteers

The pharmacokinetic and relative bioavailability studies of 20-mg enalapril tablets, the test product manufactured by Biolab, Thailand compared to the reference product (Merck Sharp & Dohme, USA) was conducted in 14 healthy Thai male volunteers following a single dose, two-period, crossover design. Each subject received 20-mg enalapril tablets of both formulations with a 1-week washout period. Plasma samples collected over a 24-h period after administration were analyzed by LC/MS/MS. Pharmacokinetic parameters were determined by using non-compartmental analysis. Regarding bioequivalence testing, the 90 per cent confidence intervals of Cmax and AUC(0-infinity) ratios (test/reference) of enalapril were 101.8-134.9 per cent and 105.9-121.4 per cent and those of enalaprilat were 104.2-122.3 per cent and 104.5-118.1 per cent. Based on the European bioequivalence guideline, the 90 per cent confidence intervals of Cmax and AUC(0-infinity) ratios of both parent and metabolite forms were within the acceptable ranges of 70-143 per cent and 80-125 per cent, respectively. It was concluded that the test formulation was bioequivalent to the reference formulation and both formulations can be used interchangeably in clinical practice.