Prevalence of Aspirin or Clopidogrel Pharmacological Resistance in Ischemic Stroke: A Step Toward Precision Medicine

BACKGROUND AND OBJECTIVES: Currently, there is not sufficient data regarding the prevalence of resistance or inadequate platelet function inhibition with the use of antiplatelet therapy in patients with noncardioembolic stroke. This study was designed to evaluate the prevalence of antiplatelet inactivity to aspirin and clopidogrel in the setting of chronic use and presentation with primary or recurrent stroke. METHODS: Patients who were taking aspirin, clopidogrel, or both at the time of presentation for stroke were selected in this study. Those with confirmed stroke on MRI or clinically determined TIA and age > 18 years were included. A standard laboratory test, VerifyNow aspirin or P2Y12 assay, was utilized to assess the responsiveness to the platelet inhibitors. A total of 158 patients were identified, 52 presenting with primary stroke and 106 with recurrent stroke. Data were analyzed using chi-squared or Fisher's exact as well as t-test analysis. RESULTS: Of the primary stroke population, 4% of patients demonstrated resistance to aspirin and 30% to clopidogrel. Of the patients presenting with recurrent stroke, 13% demonstrated resistance to aspirin and 38% to clopidogrel. The data also suggest increased resistance to aspirin and clopidogrel in Caucasians compared to minorities, with 11% versus 8% in regard to aspirin and 33% versus 17% to clopidogrel. Additionally, this study demonstrated 17% resistance to aspirin in males compared to 4% in females and 13% in males compared to 36% in females, respectively, regarding resistance to clopidogrel. No difference in inactivity to either aspirin or clopidogrel was detected between patients with stroke mechanisms of small or large vessel disease. CONCLUSIONS: The present result demonstrated that a sizeable portion of the population has inefficacious activity in the setting of specific antiplatelet agents. Additionally, sex and ethnicity differences in responsiveness to aspirin or clopidogrel have been noted. Determining a patient's response to medications could provide opportunities to individualize treatment and better prevent future strokes. Further studies of a larger scale are indeed needed to apply this information to pursue individualized treatment.