Effectiveness of reloading to overcome clopidogrel nonresponsiveness in patients with acute myocardial infarction.

Whether increasing doses of clopidogrel can overcome nonresponsiveness was evaluated. Clopidogrel nonresponsiveness was found in up to 25% of treated patients and was associated with worse prognosis in patients with acute coronary syndrome and patients undergoing coronary intervention. Adenosine diphosphate (ADP)-induced platelet aggregation was prospectively determined on day 4 of acute myocardial infarction in 200 consecutive patients, who received clopidogrel 300 mg as a loading dose and 75 mg/day thereafter. Thirty patients (15%) had ADP-induced platelet aggregation >or=80% using light transmittance aggregometry and were considered clopidogrel nonresponders. Nonresponders were reloaded with clopidogrel 600 mg, followed by 150 mg/day for 4 weeks. A 75-mg/day dose was resumed thereafter. ADP-induced platelet aggregation was reassessed 4 hours after reloading and biweekly for 10 weeks. Flow cytometry was used to determine platelet P-selectin expression and fibrinogen binding before and 4 hours after reloading. ADP-induced platelet aggregation significantly decreased 4 hours after reloading (from 83 +/- 6% to 56 +/- 14%; p <0.01). The decrease in platelet aggregation was maintained throughout the 4-week doubled maintenance dose. After resuming a maintenance dose of 75 mg/day, ADP-induced platelet aggregation returned to 66 +/- 12% (p <0.001), and 5 patients (17%) had ADP-induced platelet aggregation >or=80%. Flow cytometry showed a significant decrease in P-selectin expression (from 37 +/- 16% to 26 +/- 13%; p <0.01) and fibrinogen binding (from 84 +/- 7% to 70 +/- 13%; p <0.01) in ADP-stimulated platelets 4 hours after reloading. In conclusion, clopidogrel reloading and increased maintenance dose may overcome clopidogrel nonresponsiveness in patients with acute myocardial infarction.