Combined warfarin-aspirin therapy: what is the evidence for benefit and harm and which patients should (and should not) receive it?

Combined warfarin-aspirin therapy is currently used in about 1 million patients in North America for the long-term primary and secondary prevention of atherothrombotic and thromboembolic diseases. Despite a potentially complementary action of anticoagulant and antiplatelet drugs on different components of the thrombotic pathway, their combined use, typically with warfarin and aspirin, is not based in many cases on compelling evidence of a net therapeutic benefit. In the real-world management of patients, clinicians should combine the best available evidence with clinical judgment, considering also that, in most clinical scenarios, clinical practice guidelines may not provide strong or prescriptive recommendations for patients who should (and should not) receive combined aspirin-warfarin therapy. The objectives of this review are to describe the characteristics of patients who are receiving combined warfarin-aspirin therapy, to summarize the evidence for the therapeutic benefit and harm of combined warfarin-aspirin, and to provide practical guidelines as to which patients should (or should not) receive such treatment.