Patients with poor responsiveness to thienopyridine treatment or with diabetes have lower levels of circulating active metabolite, but their platelets respond normally to active metabolite added ex vivo

Abstract

Objectives: We evaluated the prevalence and mechanism of poor responsiveness to clopidogrel and prasugrel in coronary artery disease patients with and without diabetes.

Background: Low platelet inhibition by clopidogrel is associated with ischemic clinical events. A higher 600-mg loading dose (LD) has been advocated to increase responsiveness to clopidogrel.

Methods: In this study, 110 aspirin-treated patients were randomized to double-blind treatment with clopidogrel 600 mg LD/75 mg maintenance dose (MD) for 28 days or prasugrel 60 mg LD/10 mg MD for 28 days. Pharmacodynamic (PD) response was evaluated by light transmission aggregometry and vasodilator-stimulated phosphoprotein phosphorylation. The PD poor responsiveness was defined with 4 definitions previously associated with worse clinical outcomes. Active metabolites (AM) of clopidogrel and prasugrel were measured. Clopidogrel AM was added ex vivo.

Results: The proportion of patients with poor responsiveness was greater in the clopidogrel group for all definitions at all time points from 1 h to 29 days. Poor responders had significantly lower plasma AM levels compared with responders. Patients with diabetes were over-represented in the poor-responder groups and had significantly lower levels of AM. Platelets of both poor responders and diabetic patients responded fully to AM added ex vivo.

Conclusions: Prasugrel treatment results in significantly fewer PD poor responders compared with clopidogrel after a 600-mg clopidogrel LD and during MD. The mechanism of incomplete platelet inhibition in clopidogrel poor-responder groups and in diabetic patients is lower plasma levels of its AM and not differences in platelet P2Y(12) receptor function.