Association of type of oral anticoagulation with risk of bleeding in 45,114 patients with venous thromboembolism during initial and extended treatment-A nationwide register-based study.

Background: Safety data for different anticoagulant medications in venous thromboembolism (VTE) are scarce, in particular for extended treatment.

Objectives: To compare major bleeding rates depending on the choice of anticoagulation during initial (first 6 months) and extended treatment (6 months up to 5 years).

Methods: A nationwide register-based study including cancer-free patients with a first-time VTE between 2014 and 2020. Cox proportional hazards models were used to compare bleeding rates.

Results: We included 6558 patients on warfarin, 18,196 on rivaroxaban, and 19,498 on apixaban. At 6 months, 4750 (72.4%) remained on warfarin, 11,366 (62.5%) on rivaroxaban, and 11,940 (61.2%) on apixaban. During initial treatment, major bleeding rates were 3.86 (95% CI 3.14-4.58), 2.93 (2.55-3.31), and 1.95 (1.65-2.25) per 100 patient-years for warfarin, rivaroxaban, and apixaban, respectively, yielding adjusted hazard ratios (aHRs) of 0.89 (95% CI 0.71-1.12) for rivaroxaban versus warfarin, 0.55 (0.43-0.71) for apixaban versus warfarin, and 0.62 (0.50-0.76) for apixaban versus rivaroxaban. During extended treatment, major bleeding rates were 1.55 (1.19-1.91), 1.05 (0.85-1.26), and 0.96 (0.78-1.15) per 100 patient-years for warfarin, rivaroxaban, and apixaban, respectively, with aHRs of 0.72 (0.53-0.99) for rivaroxaban versus warfarin, 0.60 (0.44-0.82) for apixaban versus warfarin, and 0.85 (0.64-1.12) for apixaban versus rivaroxaban. Previous bleeding and increasing age were risk factors for bleeding both during initial and extended treatment.

Conclusion: Apixaban had a lower bleeding risk than warfarin or rivaroxaban during initial treatment. During extended treatment, bleeding risk was similar for apixaban and rivaroxaban, and higher with warfarin.