Comparative bioavailability of two immediate release tablets of enalapril/hydrochlorothiazide in healthy volunteers

Eur J Drug Metab Pharmacokinet. Apr-Jun 2002;27(2):91-9. doi: 10.1007/BF03190422.


A bioequivalence study of two oral formulations of 20/12.5 mg tablets of enalapril/hydrochlorothiazide was carried out in 20 healthy male volunteers according to a single dose, two-sequence, crossover randomized design. One washout period of nine days was observed between the two periods. Multiple samples were collected over 96 hours post-dosing. Bioavailability was evaluated on the basis of plasma concentrations of enalapril and its main active metabolite, enalaprilat and hydrochlorothiazide. Plasma samples were assayed for enalapril, enalaprilat and hydrochlorothiazide using a selective and sensitive high-performance liquid chromatography method with mass spectrometry detection (LC-MS). The pharmacokinetic parameter values of Cmax and tmax were obtained directly from plasma data, k(e) was estimated by log-linear regression, and AUC was calculated by trapezoidal rule. Different statistical tests were performed on the basis of untransformed and log-transformed data and the overall residual variance from ANOVA. Assuming the accepted tolerance intervals, a beta-error of 20% and 90% confidence intervals (alpha = 0.10), all the generally accepted tests (Schuirmann test and Wilcoxon-Tukey and Hauschke nonparametric tests) showed that the formulations can be considered as bioequivalent with respect to the extent of absorption, given by the AUC(0-infinity) and with respect to rate of absorption as assessed by Cmax and tmax.

Publication types

  • Clinical Trial
  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adult
  • Analysis of Variance
  • Area Under Curve
  • Biological Availability
  • Chemistry, Pharmaceutical
  • Confidence Intervals
  • Cross-Over Studies
  • Enalapril / blood
  • Enalapril / pharmacokinetics*
  • Humans
  • Hydrochlorothiazide / blood
  • Hydrochlorothiazide / pharmacokinetics*
  • Male
  • Statistics, Nonparametric
  • Tablets


  • Tablets
  • Hydrochlorothiazide
  • Enalapril