Predictors of Biochemical Aspirin and Clopidogrel Resistance in Patients With Ischemic Stroke

Variable platelet response to aspirin and clopidogrel is a well-established phenomenon in patients with coronary artery disease. We sought to determine the predictors of an impaired biochemical response to aspirin and clopidogrel in patients with ischemic stroke. Patients with established cerebrovascular disease who underwent an aspirin/clopidogrel response panel (ie, light transmittance aggregometry) between June 2003 and March 2007 were identified through an electronic database. The medical records of these patients were retrospectively reviewed, and demographic characteristics, medical history, and laboratory results were recorded. Univariate and multivariate logistic regression analyses were performed to assess for factors associated with antiplatelet resistance. Of the 465 patients included in this study, 120 (28%) were biochemical aspirin nonresponders and 83 (28%) were biochemical clopidogrel nonresponders. Of the 270 patients on dual antiplatelet therapy, 25 (9.3%) were dual biochemical nonresponders. In binary logistic regression modeling, patients with congestive heart failure (odds ratio [OR] = 4.54; 95% confidence interval [CI] = 1.33-15.5; P = .02) and those with higher hemoglobin A1c values (OR = 1.41; 95% CI = 1.12-1.79; P = .004) had a significantly greater likelihood of having a biochemical nonresponse to aspirin therapy. African-American patients (OR = 2.19; 95% CI = 1.23-3.91; P < .007) were significantly more likely to be nonresponders to clopidogrel. This preliminary study shows that aspirin and clopidogrel biochemical nonresponse frequently occurs in ischemic stroke patients. In addition, some associated variables may affect the biochemical response to antiplatelet therapy. Further study is needed to explore whether this nonresponse has an impact on clinical outcomes.