Thienopyridine-associated drug-drug interactions: pharmacologic mechanisms and clinical relevance.

The thienopyridines inhibit platelet activation and aggregation by directly inhibiting the platelet P2Y12 adenosine diphosphate receptor. The available thienopyridines are prodrugs and must be converted into active forms by the cytochrome P450 (CYP) enzyme system. An important portion of the variability in platelet response to clopidogrel is explained by the variability in plasma concentrations of the clopidogrel active metabolite. Several reports have thus progressively raised concerns about potential drug interactions as a result of inhibition or induction of CYP450 enzymes. Pharmacokinetics and pharmacodynamics studies have notably shown that concomitant use of clopidogrel and some proton pump inhibitors reduces the antiplatelet effect of clopidogrel. Several other drugs (metabolized through CYP3A4 such as statins or antifungals) similarly impact the pharmacologic response to clopidogrel. Conversely, agents that induce CYP activity increase clopidogrel responsiveness. However, the data supporting the clinical relevance of such pharmacological drug interactions have been controversial. This review will provide an overview of the mechanisms underlying thienopyridine-associated drug-drug interactions, and highlight the most recent developments in the field and propose guidance for the practitioner.