Clopidogrel is an adenosine diphosphate (ADP) receptor inhibitor. It is absorbed in an inactive form and converted to its active metabolite by the cytochrome P450 system, specifically by CYP2C19 and CYP3A4 enzymes. Some PPIs, particularly omeprazole and esomeprazole, are inhibitors of CYP2C19. Some pharmacodynamic and pharmacokinetic studies have reported reductions in platelet inhibition with concurrent use of clopidogrel and PPIs. The clinical significance of this pharmacologic interaction is unclear. Omeprazole is also known to interact with diazepam, phenytoin, and warfarin.