Sex differences in platelet reactivity in patients with myocardial infarction treated with triple antiplatelet therapy - results from assessing platelet activity in coronary heart disease (APACHE).

)Several earlier studies have reported increased risk of bleeding in women with myocardial infarction, (MI) compared to men. The reasons for the observed difference are incompletely understood, but one suggested explanation has been excess dosing of antithrombotic drugs in women. The aim of this prospective observational study was to assess sex differences in platelet activity in patients treated with three different platelet inhibitors. We recruited 125 patients (37 women and 88 men) with MI, scheduled for coronary angiography. All patients received clopidogrel and aspirin. A subgroup of patients received glycoprotein (GP) IIb/IIIa-inhibitor. Platelet aggregation in whole blood was assessed at several time points, using impedance aggregometry. Soluble P-selectin was measured 3 days after admission. There were no significant differences between women and men in baseline features or comorbidities except higher frequency of diabetes, lower hemoglobin value, and lower estimated glomerular filtration rate, in women on admission. We observed significantly more in-hospital bleeding events in women compared to men (18.9% vs. 6.8%, p = .04). There were no differences in platelet aggregation using three different agonists, reflecting treatment effect of GPIIb/IIIa-inhibitors, clopidogrel, and aspirin, 6-8 hours, 3 days, 7-9 days, or 6 months after loading dose. Moreover, there was no significant difference in soluble P-selectin. The main finding of this study was a consistent lack of difference between the sexes in platelet aggregation, using three different agonists at several time-points. Our results do not support excess dosing of anti-platelet drugs as a major explanation for increased bleeding risk in women.