Sex difference in the antiplatelet effect of aspirin in patients with stroke.

BACKGROUND: There is substantial interpatient variability in response to aspirin after an ischemic stroke or transient ischemic attack (TIA), as assessed by ex vivo effects of aspirin on platelet aggregation. The factors contributing to this variability are not well defined. OBJECTIVE: To determine whether demographic, social, or clinical characteristics are associated with ex vivo response to aspirin in patients with a history of stroke or TIA. METHODS: Eighty-one patients who were taking aspirin for secondary stroke prevention and underwent ex vivo platelet aggregation studies were identified. The medical records of eligible patients were reviewed by clinicians who specialize in the management of stroke patients. Characteristics were compared between 45 patients who had a complete response to aspirin and 36 patients who exhibited an incomplete (partial) response to aspirin based on the results of platelet aggregation testing. RESULTS: The median (range) aspirin dose was similar in complete (325; 81-1950 mg/day) and partial (325; 81-1300 mg/day) responders. There was no association between aspirin response and age, race, body mass index, medical history, smoking status, or use of statin or hormone replacement therapy. However, sex was significantly associated with response to aspirin, with more women in the partial versus complete responder group (75% vs 49%; p = 0.02). CONCLUSIONS: Our data suggest that aspirin may be less effective at inhibiting platelet aggregation in women compared with men who have a history of ischemic stroke or TIA.