Influence of H2-receptor- and proton pump inhibitors on some functions of the oxydative and conjugative drug metabolism.

There are numerous investigations describing the influence of histamine H2-receptor antagonists and proton pump inhibitors on cytochrome P450-mediated hepatic oxydative and conjugative drug metabolizing enzymes. The aim of this study was to investigate the influence of the H2-receptor blockers cimetidine, ranitidine, famotidine, nizatidine and of the proton pump inhibitors omeprazole and lansoprazole on the acetylation capacity and on different microsomal monooxygenases of the rat liver. The experiments were performed in two randomized studies with male Wistar rats after a 7-day pretreatment of the animals with antisecretory, equipotent doses of the investigational products. The activities of the arylamine N-acetyltransferase (NAT) and the microsomal enzymes were determined in vitro. Cimetidine and ranitidine decreased the activity of NAT significantly, no effect on this enzyme was observed after nizatidine. Small doses of famotidine tended to lower, high doses of famotidine tended to enhance the NAT activity. The proton pump inhibitor omeprazole significantly increased the NAT activity, lansoprazole evoked a small increase of the enzyme activity. Ethyl-resorufin O-deethylase (EROD) and penthlresorufin O-depentylase (PROD) were sensitive to cimetidine, ranitidine and famotidine. Only omeprazole and lansoprazole treatment inhibited the detromethorphan O-demethylase (DXDM) activity.