Evaluation of clopidogrel resistance in ischemic stroke patients.

OBJECTIVE Clopidogrel has potent antiplatelet effects, but recent interest has focused on clopidogrel resistance, in which platelet function is not inhibited despite taking the drug. This study evaluated clopidogrel resistance in ischemic stroke patients. METHODS After taking oral clopidogrel 75 mg/day for ≥1 week, platelet aggregometry was performed by turbidimetry in all patients, and by a screen filtration pressure method using whole blood in 37 patients. Using turbidimetry, resistance was defined as platelet maximum aggregation rate ≥34% with aggregation-inducing agent ADP 1 µmol/L, or ≥66% with ADP 4 µmol/L. Using the screen filtration pressure method, resistance was defined as a minimum concentration of ≤3 µmol/L ADP to induce secondary aggregation of platelets. PATIENTS This study was conducted in 72 patients (52 men, 20 women; mean age, 69 ± 8 years; range, 50-84 years) with non-cardiogenic ischemic cerebrovascular disease. RESULTS Based on turbidimetry, the rate of clopidogrel resistance was 8.3% with ADP 1 µmol/L and 18.1% with 4 µmol/L. Based on the screen filtration pressure, the rate of clopidogrel resistance was 8.1%. The differences between turbidimetry and screen filtration pressure methods, regarding the measurement of the presence of resistance in the same patient, were observed. CONCLUSION Clopidogrel resistance varies greatly depending on the method of measuring platelet aggregation and the definition of resistance. Rates of 8-18% were obtained using our methods and criteria.