Combination warfarin-ASA therapy: which patients should receive it, which patients should not, and why?

Combination warfarin-ASA therapy is currently used in approximately 800,000 patients in North America as long-term treatment for the primary and secondary prevention of atherothrombotic and thromboembolic diseases. Despite a potentially complementary action of anticoagulant and antiplatelet drugs, the use of combination warfarin-ASA therapy is not based on compelling evidence of a net therapeutic benefit, with the exception of patients with a mechanical heart valve. On the other hand, there is more compelling and consistent evidence that combination warfarin-ASA therapy confers a 1.5- to 2.0-fold increased risk for serious bleeding compared with use of warfarin alone. In everyday practice, clinicians should combine the best available evidence with clinical judgment, considering that in most clinical scenarios, clinical practice guideline may not provide clear recommendations for patients who should, and should not, receive combination warfarin-ASA therapy. The objectives of this review are to describe which patients are receiving combined warfarin-aspirin therapy, to summarize the evidence for the therapeutic benefit and harm of combined warfarin-ASA therapy, and to suggest practical guidelines as to which patients should, and should not, receive such treatment.