ABSTRACT
BACKGROUND: The rapid platelet function assay (RPFA) has recently been developed and used to monitor the antiplatelet effects on the P2Y12 ADP receptor. We describe the platelet response to clopidogrel and ticlopidine using the RPFA and identify the clinical factor related to laboratory resistance in patients with ischemic stroke. METHODS: Of the 172 outpatients with ischemic stroke or transient ischemic attack (TIA) enrolled in this study, 86 were taking clopidogrel (75 mg/day) and 86 were taking ticlopidine (500 mg/day). Demographic data, vascular risk factors, stroke subtypes, and the results of blood tests were recorded. Inhibition is described as the percentage change from baseline aggregation, and is calculated from the P2Y12 reaction unit (PRU) and the base PRU on the RPFA. Those patients who displayed ineffective aggregation-inhibition (inhibition <20%) on the RPFA were defined as nonresponders. RESULTS: The response of platelet aggregation-inhibition to clopidogrel and ticlopidine exhibited a variable distribution (PRU; coefficient of variability, 0.477). Ineffective platelet inhibition was detected in 25.6% of the clopidogrel group and 3.5% of the ticlopidine group (p<0.001). In addition to clopidogrel, TIA and diabetes exhibited significantly higher ineffective platelet inhibition in a univariate analysis. In the multivariate analysis, clopidogrel and TIA remained significant, and diabetes fell to borderline significance (p=0.061). CONCLUSIONS: The response to clopidogrel and ticlopidine can vary between patients. Platelet inhibition is lower for clopidogrel than for ticlopidine on the platelet function test in patients with ischemic stroke. The clinical impact of these results remains uncertain; further investigations are needed.