Background: Current guidelines recommend against using aspirin in combination with warfarin for patients with AFib, unless the patient has another indication for aspirin such as recent percutaneous coronary intervention (PCI) or a mechanical heart valve. These recommendations are based on limited clinical trial data that showed an increased risk of adverse events with combination therapy without clinical benefit. Despite these recommendations, recent studies have shown that aspirin use without a clinical indication remains common in patients taking warfarin for AFib. The prevalence of aspirin use without a clinical indication in patients taking warfarin for VTE is less well studied.
Study design: Registry-based cohort study.
Setting: Six anticoagulation clinics in Michigan.
Synopsis: Of the 6,539 patients included in the study, 2,453 patients (37.5%) were taking both warfarin and aspirin without an indication for aspirin therapy; 3,688 propensity score–matched patients (1,844 in each group) were compared to assess rates of bleeding and rates of observed thrombosis at 1 year in patients taking warfarin alone versus warfarin plus aspirin. Patients treated with warfarin plus aspirin experienced more bleeding events than did patients on warfarin monotherapy (95% confidence interval, 23.8%-28.3% vs. 95% CI, 18.3%-22.3%; P less than .001). Rates of observed thrombosis were similar between the two groups (95% CI, 1.6%-3.1% vs. 95% CI, 2.0%-3.6%; P = .40). This study demonstrates that aspirin use without a clinical indication remains common in patients taking warfarin for AFib or VTE, and that reducing inappropriate aspirin use in this patient population may help prevent adverse outcomes.
Bottom line: Use of aspirin without a clinical indication in patients taking warfarin is common and is associated with an increased risk of bleeding without significant clinical benefit.
Citation: Schaefer JK et al. Association of adding aspirin to warfarin therapy without an apparent indication with bleeding and other adverse events. JAMA Intern Med. 2019 Mar 4;179(4):533-41.
Dr. Wachter is an associate medical director at Duke Regional Hospital and an assistant professor of medicine at Duke University.