Effect of 150-mg vs 300-mg loading doses of clopidogrel on platelet function in Japanese patients undergoing coronary stent placement

Abstract

Background: The loading dose of ticlopidine is 500mg in both the US and Europe and 200mg in Japan, A lower loading dose of clopidogrel might achieve adequate platelet inhibition in Japanese patients. Methods and Results: Platelet aggregation was serially measured at baseline, and 2, 4, 6, and 8h after 150-mg (n=20) and 300-mg (n=20) clopidogrel loading. Platelets were stimulated with 5 and 20/μmol/L adenosine diphosphate (ADP) and aggregation was assessed by optical aggregometry. Pretreatment ADP-induced platelet aggregation in the 150-mg clopidogrel group did not differ from that of the 300-mg group. The administration of 300-mg clopidogrel loading dose resulted in lower platelet aggregation 2 h after the administration (5/μmol/L ADP: 53±9% vs 61±12%, p<0.05 and 20/μmol/L ADP: 61±10% vs 68±9%, p<0.05). A lower platelet aggregation induced with 20/μmol/L ADP was still observed 4h after the 300-mg clopidogrel loading (58±10% vs 65±9%, p<0.05). Conclusions: The 150-mg clopidogrel loading does not achieve rapid platelet inhibition. The 300-mg loading dose should be used to suppress platelet function rapidly even in Japanese patients undergoing coronary stent placement.