Clopidogrel Resistance and the Effect of Combination Cilostazol in Patients with Ischemic Stroke or Carotid Artery Stenting Using the VerifyNow P2Y12 Assay

OBJECTIVE: The inhibitory response to clopidogrel considerably varies among individuals and clopidogrel resistance is a risk factor for thrombotic events in patients with cardiovascular disease. Based on the platelet aggregation evaluated by the VerifyNow P2Y12 Assay, the present study investigated clopidogrel resistance and the effect of cilostazol addition. METHODS: We measured the ability of 20 µM ADP to aggregate platelets using the VerifyNow P2Y12 Assay. Clopidogrel resistance was defined as % inhibition of <20% in this assay. PATIENTS: We examined 77 patients (53 men and 24 women, aged 65.8 ± 9.9 years) with ischemic stroke or carotid artery stenting who received clopidogrel (75 mg) for >7 days at our hospital between October 2009 and March 2010. For 62 patients (42 men and 20 women, aged 65.3 ± 9.9 years) 75 mg clopidogrel alone was administered (clopidogrel only group); the other 15 patients (11 men and 4 women, aged 67.9 ± 9.9 years) received 75 mg of clopidogrel plus 100 or 200 mg of cilostazol (cilostazol combination group). RESULTS: Clopidogrel resistance was identified in 18 (29%) of the 62 patients in the clopidogrel only group. The percent inhibition was significantly higher in the cilostazol combination group than in the clopidogrel only group (41.7 ± 28.0% vs. 64.9 ± 22.7%, p=0.005). None of the patients in the cilostazol combination group had % inhibition of <20%. CONCLUSION: Clopidogrel resistance developed in 29% of patients given clopidogrel alone. The addition of cilostazol to clopidogrel may have intensified platelet inhibition.