Absolute bioavailability of cimetidine tablets in healthy volunteers

Abstract

This study consists of two parts. In the first part, five different brands of 400 mg cimetidine tablets marketed in Thailand were evaluated. In Vitro studies demonstrated that all products met the British Pharmacopoeia 1980 for disintegration time specifications, and only 3 brands (A, B and C) met the United State Pharmacopoeia XXI,3rd Supplement for dissolution time specifications and no significant differences in dissolution rate constants among these 3 brands were observed. Only cimetidine tablet Brand B, the local manufactured brand with lowest retail price, were selected for In Vivo studies compared with the original brand (Brand A). In the second part, the absolute and the relative bioavailabilities of 400 mg cimetidine tablets were studied in 9 Thai healthy volunteers using a crossover design. Plasma levels were determined by a specifically high pressure liquid chromatographic method. Individual plasma profile was analyzed according to noncompartmental method. The effective plasma half-life of cimetidine was 1.31 ± 0.09 hours. The area under the plasma concentration-time profiles of cimetidine after administration of 200 mg injection was 8.19 ± 0.39 µg-hr/ml and those after administration of 400 mg tablets were 12.51 ± 0.83 µg-hr/ml for tablet Brand A and 11.24 ± 0.71 µg-hr/ml for tablet Brand B. The mean absorption rate constant ranged from 0.67± 0.11 to 0.90 ± 0.18 per hour and the time for which the plasma levels remained above 0.5 µg/ml was approximately 6.3 hours. There were no statistically significant differences between these related pharmacokinetic parameters of Brands B and A. The absolute bioavailabilities were found to be 76.13 ± 3.54 percent for tablet Brand A and 71.15 ± 4.62 percent for tablet Brand B. The relative bioavailability of Brand B with respect to Brand A was 94.23 ± 6.54 percent, referring that cimetidine tablets of Brand B and Brand A were bioequivalent.