The Predictive Value Of The Response To Clopidogrel Demi-loading Dose For Clopidogrel Resistance

Objective: Clopidogrel is a new thienopyridine derivative, and it is a prodrug, can be absorbed by intestinal tract after oral administration, 85% of the total was hydrolyzed into inactive carboxylic acid derivative by esterase, a fraction was transformed into the active sulfhydryl compounds by cytochrome P450 monooxygenase enzymes. The active sulfhydryl compounds can irreversibly combine with the adenosine diphosphate (ADP) receptor (P₂Y₁₂) of platelet membrane surface, leading to fibrinogen binding site of glycoprotein proteinâ…¡b /â…¢a (GPâ…¡b /â…¢a) receptor coupled with P₂Y₁₂ of platelet membrane can not be exposed, selectively and irreversibly inhibits ADP-induced platelet aggregation.Clopidogrel as one of a clinically standard dual antiplatelet drugs plays a fundamental role in the treatment of patients with coronary artery disease. But in recent years many studies found that the response of patients to clopidogrel manifests extensive individual differences, some patients behave of poor response or no response to clopidogrel. The phenomenon of low response or no response to clopidogrel is known as clopidogrel resistance. Patients of clopidogrel resistance with conventional doses of clopidogrel can not effectively inhibit platelet aggregation and reduce the incidence rate of thrombotic complications and other adverse clinical events.At present, there is no uniform standard for the definition of clopidogrel resistance, ADP induced platelet aggregation was a simple, shortcut and the best of specificity index to reflect the anti-platelet effective, can work as a major monitoring indicator. Lau, etc. defined clopidogrel nonresponders, low responders, and responders by a relative inhibition of ADP (20 umol/L) induced platelet aggregation of <10%, 10% to 29%, and >or=30%, respectively. It is now internationally generally accepted definition of clopidogrel resistance, used as the gold standard in this study.Many methods detecting of clopidogrel resistance have been reported in the literature, but no predictive index of clopidogrel resistance has been seen. Therefore, it is of great significance if a predictive index was determined, which may contribute to guide individual treatment, improve the effectiveness of anti-platelet therapy and reduce the incidence of adverse cardiovascular events.The aim of this current study is to observe whether platelet reactivity after taking clopidogrel 150mg within 12 to 18 hours can predict clopidogrel resistance in acute coronary syndrome (ACS) patients. Using of ROC analysis to determine a optimal cut-off point, drawing ROC curve, and evaluating the accuracy of the predictor by area under the curve.Methods: A total of 138 acute coronary syndrome patients were selected between October 2009 and December 2010, including 92 males and 46 females, with a mean age of 58.13±10.10 years. All selected subjects are diagnosed acute coronary syndrome (ACS) patients (with typical clinical symptoms, electrocardiographic changes, indicated myocardial enzymes or testified by coronary angiography). Blood samples were obtained through venipuncture in the cubital vein before loading dose clopidogrel 150mg administration (baseline), within 12 to 18 hours after loading dose clopidogrel administration and at the fourth days after clopidogrel administration, for measuring platelet aggregation induced by 10umol/L and 20umol/L ADP. Clopidogrel nonresponders and Clopidogrel responders are divided by difference between the baseline and steady-state platelet aggregation according to the standard of Lau, etc. defined Clopidogrel nonresponders, and compute the difference between baseline platelet aggregation and platelet aggregation after loading dose clopidogrel administration. SPSS 13.0 software was used for statistical analysis. Measurement data showed a normal distribution was expressed as the mean±standard deviation (SD), and the comparison between two groups using two-sample t test, measurement data showed a skewed distribution was expressed as the median (M) and interquartile range ( QR), and comparison among groups using nonparametric test (rank sum test). Enumeration data was expressed as rate (%), and comparison among groups using Chi-square test. The influence of clinical baseline factors was evaluated by stepwise binary logistic regression analysis. A optimal cut-off point was determined by ROC analysis, and draw ROC curve, evaluating the accuracy of diagnostic systems with area under the curve. A p value of < 0.05 was considered statistically significant.Results: Clopidogrel resistance was defined by a relative inhibition of ADP (10 umol/L or 20 umol/L) induced platelet aggregation of <10%. Among the 138 patients, male is ninety two(66.7%) ,and female is forty six(33.3%). At the fourth days after clopidogrel administration, 29 (21.01%) patients were found clopidogrel resistance by measuring ADP (10μmol/L) induced platelet aggregation, and the others was responders (78.99%); 24(17.39%) patients were found clopidogrel resistance by measuring ADP (20μmol/L) induced platelet aggregation, and the others was responders(82.6%).Using 10 umol/L ADP and 20 umol/L ADP as inducer respectively, platelet aggregation between clopidogrel nonresponders and clopidogrel responders was not significantly different before clopidogrel administration and after clopidogrel administration within 12-18 hours, but was significantly different at the fourth days after clopidogrel administration; platelet aggregation of clopidogrel nonresponders was not significantly different among before, within 12-18 hours and the fourth days after clopidogrel administration; but platelet aggregation of clopidogrel responders was significantly different among before, within 12-18 hours and the fourth days after clopidogrel administration.Using 10 umol/L ADP as inducer, the optical cut-off point was 7.5ohms determined by ROC analysis of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration, the sensitivity evaluating clopidogrel nonresponders by the cut-off point was 44.80%, and the specificity was 72.50%, area under the ROC curve was 0.607(95% CI:0.494,0.720)(P=0.077); the optical cut-off point was 0.5ohms determined by ROC analysis of the decreasing values of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration compared with baseline values, the sensitivity evaluating clopidogrel nonresponders by the cut-off point was 84.40%, and specificity was 86.20%, area under the ROC curve was 0.891(95% CI:0.828,0.953)(P<0.001); the optical cut-off point was 12.22% determined by ROC analysis of the decreasing percentage of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration, the sensitivity evaluating clopidogrel nonresponders by the cut-off point was 82.60%, and the specificity was 89.70%, area under the ROC curve was 0.884(95% CI:0.814,0.954)(P<0.001). Using 20 umol/L ADP as inducer, the optical cut-off point was 5.5ohms determined by ROC analysis of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration, the sensitivity evaluating clopidogrel nonresponders by the cut-off point was 70.80%, and specificity was 55.30%, area under the ROC curve was 0.609(95% CI:0.487,0.731)(P=0.094); the optical cut-off point was 0.5ohms determined by ROC analysis of the decreasing values of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration compared to baseline values, the sensitivity evaluating clopidogrel nonresponders by the cut-off point was 85.10%,and the specificity was 75.00%, area under the ROC curve was 0.842(95% CI:0.755,0.929)(P<0.001); the optical cut-off point was 16.03% determined by ROC analysis of the decreasing percentage of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration compared with baseline values, the sensitivity evaluating clopidogrel nonresponders by the cut-off point was 78.10%, and specificity was 83.30%, area under the ROC curve was 0.826(95% CI:0.724,0.928)(P<0.001).Analyzing the sex, age, body mass index (BMI), smoking history, drinking history, hypertension, hyperlipidemia, diabetes mellitus, the concomitant drugs use including PPI, statins, ACEI, CCB, and ARB agent and the decreasing percentage of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration compared with baseline values relating of clopidogrel resistance, by stepwise binary logistic regression analysis. The outcome displayed the risk of clopidogrel resistance was 55.196 times higher than the others(P<0.001)when the decreasing percentage of platelet aggregation was lower than 12.22% induced by 10 umol/L ADP; and the risk of clopidogrel resistance was 19.643 times higher than the others(P<0.001) when the decreasing percentage of platelet aggregation was lower than 16.03% induced by 20 umol/L ADP; but the other factors were not significantly different between clopidogrel resistance group and non-clopidogrel resistance group.Conclusion: Using 10 umol/L ADP and 20 umol/L ADP as inducer respectively, the value of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration can not predict clopidogrel resistance; but to some extent the difference between this value and baseline value and the decreasing percentage of platelet aggregation within 12-18 hours after demi-loading dose clopidogrel administration compared with baseline values can predict clopidogrel resistance.