1 The in vitro metabolism of omeprazole was studied in human liver microsomes in order to define the metabolic pathways and identify the cytochrome P450 (CYP) isoforms responsible for the formation of the major omeprazole metabolites. content. Inhibition studies with isoform selective inhibitors also indicated a dominant role of S-mephenytoin hydroxylase with some CYP3A contribution in the formation of hydroxyomeprazole. Correlation and inhibition data for the sulphone and metabolite X were consistent with a predominant role of the CYP3A subfamily in formation of these metabolites. Formation of 5-0-desmethylomeprazole was inhibited by both R, S-mephenytoin and quinidine, indicating that both S-mephenytoin hydroxylase and CYP2D6 may mediate this reaction in human liver microsomes and in vivo. 4 The Vmax/Km (indicator of intrinsic clearance in vivo) for hydroxyomeprazole was four times greater than that for omeprazole sulphone. Consistent with findings in vivo, the results predict that omeprazole clearance in vivo would be reduced in poor metabolisers of mephenytoin due to reduction in the dominant partial metabolic clearance to hydroxyomeprazole.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.