Low-dose aspirin and risk of intracranial bleeds An observational study in UK general practice

Objective: To quantify the risk of intracranial bleeds (ICBs) associated with new use of prophylactic low-dose aspirin using a population-based primary care database in the United Kingdom. Methods: A cohort of new users of low-dose aspirin (75-300 mg; n = 199,079) aged 40-84 years and a 1: 1 matched cohort of nonusers of low-dose aspirin at baseline were followed (maximum 14 years, median 5.4 years) to identify incident cases of ICB, with validation by manual review of patient records or linkage to hospitalization data. Using 10,000 frequency-matched controls, adjusted rate ratios (RRs) with 95% confidence intervals (CIs) were calculated for current low-dose aspirin use (0-7 days before the index date [ICB date for cases, random date for controls]); reference group was never used. Results: There were 1,611 cases of ICB (n = 743 for intracerebral hemorrhage [ICH], n = 483 for subdural hematoma [SDH], and n = 385 for subarachnoid hemorrhage [SAH]). RRs (95% CI) were 0.98 (0.84-1.13) for all ICB, 0.98 (0.80-1.20) for ICH, 1.23 (0.95-1.59) for SDH, and 0.77 (0.58-1.01) for SAH. No duration of use or dose-response association was apparent. RRs (95% CI) for >= 1 year of low-dose aspirin use were 0.90 (0.72-1.13) for ICH, 1.20 (0.91-1.57) for SDH, and 0.69 (0.50-0.94) for SAH. Conclusion: Low-dose aspirin is not associated with an increased risk of any type of ICB and is associated with a significantly decreased risk of SAH when used for >= 1 year.