The dose of aspirin for the prevention of cardiovascular and cerebrovascular events

Background: Low dose aspirin (ASA) (75-325 mg daily) is commonly used for the secondary prevention of cardiovascular and cerebrovascular events, as recommended by US national guidelines. Questions remain, however, as to whether there is a difference in the efficacy and safety across this low dose range. Scope: Double-blind controlled studies, meta-analyses, and observational analyses were reviewed to assess the body of evidence regarding the safety and efficacy of aspirin dosing. Findings: Only one double-blind study directly compared two doses of aspirin within the recommended low dose range. No difference in efficacy or safety was observed, although there was a trend toward greater efficacy with ASA 325 mg vs. ASA 81 mg. Three meta-analyses did not find a difference in bleeding events within the low dose range, while one found that higher doses were associated with more events. One meta-analysis found ASA 75-150 mg was as effective as ASA 160-325 mg. Observational analyses of low dose (75-325 mg) ASA from two large controlled trials differed in their results. One study found no difference in the number of cardiovascular/cerebrovascular events, and a significant improvement in mortality with higher doses, while the other found that higher doses were associated with more events. Conclusion: There does not appear to be a difference in safety across the low dose range of 75-325 mg based on randomized controlled trial data. Furthermore, ASA 325 mg daily appears to be at least as effective as 75 mg daily. Since the optimal dose of ASA for primary and secondary prevention of events in the broad population is uncertain, dosing considerations should include an evaluation of a patient's individual clinical status as well as an overall cardiovascular and cerebrovascular benefit vs. risk assessment.