Increased risk of intracranial hemorrhage when aspirin is combined with warfarin: A meta-analysis and hypothesis

Background: Oral anticoagulation with vitamin K antagonists increases the r isk of intracranial hemorrhage; whether addition of aspirin to oral anticoa gulation augments this risk is unclear, Methods: Meta-analysis of randomize d clinical trials in which aspirin was added to oral anticoagulants, Result s: Six randomized clinical trials were identified, including a total of 3,8 74 participants, Use of aspirin with oral anticoagulants was associated wit h more than double the frequency of intracranial hemorrhage (relative risk = 2.4, 95% Cl = 1.2-4.8, p = 0.02). Conclusion: We hypothesize that aspirin when added to oral vitamin K antagonists may increase the risk of intracra nial hemorrhage, but this observation requires confirmation. The magnitude of this effect is uncertain, and the clinical importance is likely differen t for different patient populations.