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

Abstract

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.