Measurement of the effect of ticlopidine with the platelet function analyser (pfa-100) during coronary stent implantation
Article Outline
To the Editor:
I read with great interest the papers of Madan et al.1, 2 They studied platelet function during percutaneous coronary intervention (PCI) with the platelet function analyser (PFA-100). All patients received glycoprotein IIb/IIIa inhibitors (abciximab or eptibibatide), aspirin, and heparin. Patients undergoing stent implantation also received ticlopidine on the evening before PCI or on the morning of the PCI. The PFA-100 detected maximal platelet inhibition immediately after administration of the glycoprotein IIb/IIIa inhibitors bolus and during the course of infusion. Twelve hours after discontinuation of abciximab infusion, they observed that platelet function had already normalized with a high degree of interpatient variability. This variability among individuals in recovery from platelet inhibition may be related to the lack of concordance between ticlopidine pharmacodynamics and the time point of measurement. Ticlopidine has an onset-of-activity of between 24 and 48 hours, and its maximum activity occurs after 3 to 5 days.3 Moreover, the authors presented the PFA-100 as a device sensitive in the evaluation of platelet inhibition seen with ticlopidine. This is not true. The PFA-100 is a test-cartridge system. Citrated whole blood is aspirated through a capillary (under high shear conditions) into an aperture, the surface of which is coated with collagen and epinephrine or collagen and adenosine diphosphate (ADP). Platelets adhere, aggregate, and occlude the aperture. The instrument determines the time from the start of the test until the platelet plug occludes the aperture, and reports that time interval as the closure time. The PFA-100 results are not affected by heparin and there is no influence of aspirin on the collagen/ADP closure time.4, 5 The collagen/ADP cartridge has a high local concentration of ADP (50 μg adenosine-5′-diphosphate), and this may also explain the lack of ticlopidine effect on the PFA-100.6
References
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PII: S0002-8703(03)00178-9
doi:10.1016/S0002-8703(03)00178-9
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