Ozagrel hydrochloride monohydrate, a thromboxane synthase inhibitor, and its metabolites as inhibitors of hepatic microsomal drug metabolism.

The change in the hepatic oxidative drug-metabolizing capacity in humans treated with ozagrel hydrochloride monohydrate (OZA), an imidazole derivative and a new thromboxane A2 synthase inhibitor, was studied and the inhibitory potencies of the metabolites of OZA (M-1 and M-2) on the mouse hepatic microsomal monooxygenase system in vitro were compared with that of OZA. In vitro, M-1 and M-2, which are the beta-oxidized form and the reduced form of OZA, respectively, inhibited aminopyrine N-demethylation, aniline hydroxylation and testosterone hydroxylations in mouse hepatic microsomes and produced type II difference spectra in the same manner as OZA. The kinetic data indicated that the inhibitory potencies and the affinities of these compounds for cytochrome P-450 were decreased in the order of M-2 greater than OZA greater than M-1. The ratio of 6 beta-hydroxycortisol (6 beta-OHF) to cortisol (F) in urine, used as an indicator of oxidative drug-metabolizing capacity in humans, did not change significantly during oral treatment with 400 mg/d of OZA, while the ratio decreased to 80-85% of the original level during treatment with 800 mg/d of OZA. Although the participation of the metabolites of OZA in the reduction of drug-metabolizing capacity in vivo is not yet clear, the results suggest that hepatic oxidative drug-metabolizing enzyme activities in humans are inhibited by treatment with a relatively high dose of OZA.