Abstract 2: Comparative Effectiveness and Safety of Anticoagulant Therapy With Warfarin, Dabigatran, Apixaban, or Rivaroxaban in Patients With Nonvalvular Atrial Fibrillation

Abstract

Background: The efficacy and safety of novel oral anticoagulants (NOACs) as alternatives to warfarin therapy in nonvalvular atrial fibrillation (NVAF) patients have been studied in randomized trials. Given the increasing use of NOACs, additional data is required to assess the relative effectiveness and safety of anticoagulation with warfarin, dabigatran, apixaban, or rivaroxaban therapy in real-world settings in the United States (U.S). Methods: A retrospective cohort study design was used to analyze data from a U.S. commercial claims database of > 38 million members. Study population included new users of warfarin, dabigatran, apixaban, or rivaroxaban aged ≥ 18 years with ≥ 2 diagnoses of NVAF from November 2010 to February 2015. The primary effectiveness outcome was a composite of thromboembolic event or stroke; the primary safety outcome was major bleeding event requiring hospitalization. Cox proportional hazards models with inverse probability of treatment weighting (IPTW) were used to compare event rates between NOAC and warfarin users, and among NOAC users. Results: In the final NVAF cohort studied, there were 23,431 warfarin, 8,539 dabigatran, 3,689 apixaban, and 8,398 rivaroxaban users. A total of 7,022 primary outcome events and 3,264 safety events were identified. Warfarin users were older than dabigatran, apixaban, or rivaroxaban users (mean: 73 vs 66 vs 69 vs 67 years). After IPTW, all treatment groups were balanced on all baseline risk factors including stroke and bleeding risk. Compared to warfarin, NOAC users had fewer thromboembolic events or strokes: dabigatran (hazard ratio HR, 0.77 [95% CI: 0.72 - 0.82]), apixaban (HR, 0.73 [CI: 0.65 - 0.82]), and rivaroxaban (HR, 0.80 [CI: 0.75 - 0.86]). Additionally, dabigatran ([HR], 0.67 [CI: 0.60 - 0.76]), and apixaban users (HR, 0.52 [CI: 0.41 - 0.67) experienced fewer major bleeding events compared to warfarin users. No significant difference was found in major bleeding risk between rivaroxaban (HR, 1.00 [CI: 0.89 - 1.12]) and warfarin users. All three NOAC groups had similar risks for thromboembolic event or stroke: dabigatran vs rivaroxaban (HR, 0.96 [CI: 0.88 - 1.05]); apixaban vs rivaroxaban (HR, 0.91 [CI: 0.80 - 1.04]); dabigatran vs apixaban (HR, 1.05 [CI: 0.93 - 1.19]). However, compared to rivaroxaban users, major bleeding risk was 33% and 48% lower in dabigatran and apixaban users respectively (HR, 0.67[CI: 0.58 - 0.78]) and HR, 0.52 [CI: 0.40 - 0.68]). Conclusions: Our results demonstrated a lower risk of a thromboembolic event or stroke among dabigatran, apixaban, or rivaroxaban users compared to warfarin users. Among NOACs, risks of a thromboembolic event or stroke were similar. Further studies are needed to clarify the finding of a higher major bleeding risk in warfarin and rivaroxaban users.