Patients receiving chronic clopidogrel therapy undergoing nonemergent percutaneous coronary intervention who exhibit high on-treatment ADP-induced platelet aggregation are at increased risk for postprocedural ischemic events. These findings might have implications for the alteration in clopidogrel maintenance dose and use of glycoprotein IIb/IIIa inhibitors in selected patients.

Clopidogrel therapy in CS is associated with increased platelet inhibition and lower aggregation as compared with NS. The mechanism of the smoking effect deserves further study and may be an important cause of response variability to clopidogrel therapy.

OBJECTIVE-Diabetic patients may have a higher prevalence of platelet aspirin resistance than nondiabetic patients. Our goal was to analyze platelet aspirin responsiveness to various aspirin doses in diabetic and nondiabetic patients. RESEARCH DESIGN AND METHODS-We examined the effect of aspirin (81, 162, and 325 mg/day for 4 weeks each) on platelet aspirin responsiveness in 120 stable outpatients (30 diabetic patients and 90 nondiabetic patients) with coronary artery disease (CAD) using light transmittance aggregometry (LTA), VerifyNow, platelet function analyzer (PFA)-100, and levels of urinary 11-dehydro-thromboxane B 2 (11-dh-TxB 2 ).RESULTS-In the total group, a low prevalence (0 -2%) of aspirin resistance was observed with all aspirin doses as determined by arachidonic acid-induced LTA. Aspirin resistance was higher at the 81-mg dose in diabetic versus nondiabetic patients using collagen-induced LTA (27 vs. 4%, P ϭ 0.001), VerifyNow (13 vs. 3%, P ϭ 0.05), and urinary 11-dh-TxB 2 (37 vs. 17%, P ϭ 0.03). Diabetic patients treated with 81 mg exhibited higher platelet function measured by VerifyNow, collagen-and ADP-induced LTA, and 11-dh-TxB 2 levels (P Յ 0.02 for all comparisons). Higher aspirin doses significantly inhibited platelet function and decreased aspirin resistance in diabetic patients (P Ͻ 0.05).CONCLUSIONS-Diabetic patients with CAD treated with 81 mg aspirin exhibit a higher prevalence of aspirin resistance and have significantly higher ADP-and collagen-induced platelet aggregation, 11-dh-TxB 2 levels, and aspirin reaction units measured by VerifyNow than nondiabetic patients. Increased aspirin dosing resulted in similar rates of resistance and platelet function levels between groups. These findings indicate that diabetic patients exhibit a global high platelet reactivity phenotype that may be partially overcome by higher aspirin doses. Diabetes 56: 3014-3019, 2007

Background-Post-stenting ischemic events occur despite dual antiplatelet therapy suggesting that a "one size fits all" antithrombotic strategy has significant limitations. Ex vivo platelet function measurements may facilitate risk stratification and personalized antiplatelet therapy.

Background-The antiplatelet effect of aspirin is attributed to platelet cyclooxygenase-1 inhibition. Controversy exists on the prevalence of platelet resistance to aspirin in patients with coronary artery disease and effects of aspirin dose on inhibition. Our primary aim was to determine the degree of platelet aspirin responsiveness in patients, as measured by commonly used methods, and to study the relation of aspirin dose to platelet inhibition. Methods and Results-We prospectively studied the effect of aspirin dosing on platelet function in 125 stable outpatients with coronary artery disease randomized in a double-blind, double-crossover investigation (81, 162, and 325 mg/d for 4 weeks each over a 12-week period). At all doses of aspirin, platelet function was low as indicated by arachidonic acid (AA)-induced light transmittance aggregation, thrombelastography, and VerifyNow. At any 1 dose, resistance to aspirin was 0% to 6% in the overall group when AA was used as the agonist, whereas it was 1% to 27% by other methods [collagen and ADP-induced light transmittance aggregation, platelet function analyzer (PFA-100)]. Platelet response to aspirin as measured by collagen-induced light transmittance aggregation, ADP-induced light transmittance aggregation, PFA-100 (81 mg versus 162 mg, PՅ0.05), and urinary 11-dehydrothromboxane B 2 was dose-related (81 mg versus 325 mg, Pϭ0.003). No carryover effects were observed. Conclusions-The assessment of aspirin resistance is highly assay-dependent; aspirin is an effective blocker of AA-induced platelet function at all doses, whereas higher estimates of resistance were observed with methods that do not use AA as the stimulus. The observation of dose-dependent effects despite nearly complete inhibition of AA-induced aggregation suggests that aspirin may exert antiplatelet properties through non-cyclooxygenase-1 pathways and deserves further investigation. (Circulation. 2007;115:3156-3164.)