Onset and extent of platelet inhibition by clopidogrel loading in patients undergoing elective coronary stenting: The Plavix Reduction Of New Thrombus Occurrence (PRONTO) trial

Background Despite the common practice of clopidogrel loading for coronary stenting, the time dependence and degree of platelet inhibition after this therapy are not well defined. We sought to establish an optimal clopidogrel dosing regimen for sustained platelet inhibition in stented patients. Methods and Results Platelets were assessed by conventional aggregation with 5 mumol/L adenosine diphosphate (ADP), 1 mug/mL collagen (COLL), and 750 mumol/L arachidonic acid; whole blood aggregation by 1 mug/mL collagen (WBA); shear-induced closure time (CT); contractile force (CF); and expression of 9 surface receptors by flow cytometry in 100 patients undergoing elective stent placement without glycoprotein (GP) IIb/IIIa receptor antagonists. Blood was obtained at baseline and serially over 5 days poststenting after different clopidogrel loading regimens: 300 mg 24 hours before (Group A), 12 hours before (Group B), 3, to 6 hours before (Group C), and 75 mg at the time of intervention (Group D). Before stenting, ADP, COLL, CT, and WBA were reduced by clopidogrel loading (P < .05). CF was not affected by clopidogrel. Before stenting, GP IIb/IIIa expression increased in groups A through C (P < .05), whereas PE-CAM-1 and CD107a were reduced (P < .05). At 2 hours and 2 days poststenting, platelets, in general, exhibited an increase in activity that was most inhibited by clopidogrel loading. Clopidogrel inhibited GP Ib, platelet/endothelial cell adhesion molecule-1, CD 107a, CD 151, and GP IIb/IIIa expression at day 5 poststenting. Conclusion A 300 mg clopidogrel load given 3 to 24 hours before stenting inhibits platelets at the time of the procedure and reduces poststent activity more than a 75 mg dose given at the time of the procedure. The inhibition of adhesive molecule expression may also contribute an antithrombotic effect. Poststent activation of platelets may warrant higher periprocedural dosing.