Sex differences in spontaneous reports on adverse bleeding events of antithrombotic treatment

To explore if sex differences are found in spontaneously reported adverse events for clopidogrel, low-dose aspirin and warfarin treatment in routine care. A cross-sectional analysis combining data on bleeding events from the Swedish Spontaneous Adverse Drug Event Reporting System (SWEDIS) with data from the National Prescribed Drug register. Bleeding event reports from 1999 to 2010 and 2005 to 2010 were adjusted to the number of prescriptions and the number of exposed patients respectively among women and men. Co-medication and co-prescription were analysed. More men were dispensed clopidogrel although the reported bleeding event risk after adjustment for number of patients exposed was higher in women (RR 1.40; 95 % CI, 1.00-1.96). The difference disappeared when adjusting for the number of prescriptions (RR 0.99; 95 % CI, 0.71-1.39). The reported bleeding event risk with low-dose aspirin was lower in women, adjusted for patients exposed (RR 0.80; 95 % CI, 0.66-0.97). For warfarin, no sex difference in bleeding event reports could be found (RR 1.01; 95 % CI, 0.87-1.17). This ecological comparison of bleeding reports and dispensed prescriptions showed a signal towards a higher prevalence of bleeding reports in women on clopidogrel treatment while the opposite was found for low-dose aspirin. For warfarin, no significant sex difference was seen regarding bleeding event reports, suggesting individualised dosing being an important factor. Men were more commonly prescribed antithrombotic combinations, and this was reflected by a larger proportion of bleeding reports including more than one antithrombotic agent.