Clopidogrel-induced platelet inhibition cannot be detected by the platelet function analyzer-100 system in stroke patients.

The administration of an adenosine diphosphate (ADP) receptor antagonist, such as clopidogrel, is recommended for recurrent stroke patients under aspirin treatment. However, up to 25% of vascular patients have an inadequate response to clopidogrel treatment, which could be associated with increased reinfarction rates. This study investigated whether the platelet function analyzer (PFA-100) system represents an appropriate tool for monitoring clopidogrel's antiplatelet effects in stroke patients. Sixteen stroke patients on clopidogrel therapy (75 mg/day) were included in a prospective analyst-blinded, cross-sectional study. Platelet function was assayed by collagen/epinephrine (CEPI)- and collagen/ADP (CADP)-induced closure times (CTs) using the PFA-100 system. von Willebrand factor antigen (vWF-Ag) levels were measured by enzyme immunoassay. CEPI-CT and CADP-CT values averaged 160 +/- 15 seconds and 102 +/- 10 seconds, respectively, and were in the normal range. vWF-Ag concentrations averaged 153 +/- 17% and correlated inversely with CTs (r = .71; P < .002 for CEPI-CT, r = .54; P < .04 for CADP-CT). Our data indicate that the current PFA-100 cartridges are not sufficiently sensitive to detect clopidogrel-induced platelet inhibition in stroke patients.