Abstract 138: Effectiveness and Safety of Apixaban Compared to Warfarin among Venous Thromboembolism Patients in the United States Medicare Population

Background: The AMPLIFY randomized clinical trial showed that apixaban was associated with significantly lower major bleeding (MB) compared to warfarin for patients with venous thromboembolism (VTE). The main objective of this study was to compare the risk of major bleeding (MB), clinically relevant non-major bleeding (CRNM), and recurrent VTE among VTE patients treated with apixaban vs warfarin in the US Medicare population. Methods: Patients (aged ≥65 years) prescribed apixaban or warfarin within 30 days following a VTE event diagnosed in hospital or ambulatory setting were identified from 01SEPT2014-31DEC2016 using 100% CMS Medicare data. The first apixaban or warfarin prescription claim outside of the hospital was defined as the index date. Patients were required to have had continuous health plan enrollment for 6 months and no parenteral or oral anticoagulant use before the index VTE event. Outcomes were assessed from index date to the earliest of discontinuation, switch, health plan disenrollment, death, 6 months post-index date, or 31DEC2016. One-to-one propensity score matching (PSM) was used to balance patient characteristics. Cox proportional hazard models were used to estimate the risk of MB, CRNM bleeding, and recurrent VTE. Results: Among 37,799 patients meeting inclusion criteria, 25,284 patients initiated warfarin (66.9%) and 12,515 patients initiated apixaban (33.1%). Post-PSM, 11,363 matched pairs of apixaban-warfarin patients were identified, with a mean follow-up period of 4.0 and 4.4 months. Mean age was 78 years; nearly 37% of patients were male with a mean Charlson Comorbidity Index score of 2.9 in both groups. Apixaban was associated with a lower risk of MB (HR: 0.76; 95% CI: 0.64-0.91) and CRNM bleeding (HR: 0.77; 95% CI: 0.70-0.84) compared to warfarin. The risk of recurrent VTE was similar among apixaban and warfarin patients (HR: 1.04; 95% CI: 0.75-1.43; Figure). Conclusions: Among US Medicare patients with VTE, apixaban was associated with a lower risk of MB and CRNM bleeding and similar risk of recurrent VTE compared to warfarin. These results may be supportive in evaluating the risk-benefit ratio of apixaban for treatment of elderly VTE patients.