Serial Changes in Platelet Activation in Patients With Unstable Angina Following Coronary Stenting : Evaluation of the Effect of Clopidogrel Loading Dose in Inhibiting Platelet Activation

Background Platelet activation is crucial in the development of acute or subacute stent thrombosis following implantation. This study investigated whether a conventional regimen comprising a loading dose of 300mg of clopidogrel, followed by daily doses of 75mg, could significantly suppress platelet activation in patients with unstable angina (UA) undergoing coronary stenting. Methods and Results Platelet activation (expressed by CD62p) was serially examined using flow cytometry in 42 consecutive patients with UA who underwent coronary stenting. CD62p expression was also evaluated in 30 normal control subjects. CD62p expression was markedly higher pre-procedure in the study patients than in the normal control subjects (5.2±4.0% vs 1.4±0.6%, p<0.0001). CD62p expression in the study patients remained significantly higher at 24h after the procedure than in the control subjects (3.8±2.1% vs 1.4±0.6%, p<0.001). Additionally, only 26% of CD62p expression (5.2% vs 3.8%, p=0.026) in the study patients was suppressed at 24h after the procedure. However, more than 60% of CD62p expression (5.2% vs 2.0%, p<0.0001) was suppressed on day 7 after the procedure. Conclusion Less than one-third of CD62p expression was suppressed at 24h by the conventional loading dose (300mg) of clopidogrel in patients with UA following coronary stenting. This finding indicates the need to evaluate whether an increased loading dose of clopidogrel would be a more efficacious and safe regimen for patients in this clinical setting.