Background— Dabigatran 150 and 110 mg twice a day and warfarin are effective for stroke prevention in atrial fibrillation. The purpose of this study was to compare their risks of bleeding in the Randomized Evaluation of Long-Term Anticoagulant Therapy (RE-LY) trial. Methods and Results— The RE-LY trial randomized 18 113 patients to receive dabigatran 110 or 150 mg twice a day or warfarin dose adjusted to an international normalized ratio of 2.0 to 3.0 for a median follow-up of 2.0 years. Compared with warfarin, dabigatran 110 mg twice a day was associated with a lower risk of major bleeding (2.87% versus 3.57%; P =0.002), whereas dabigatran 150 mg twice a day was associated with a similar risk of major bleeding (3.31% versus 3.57%; P =0.32). There was a significant treatment-by-age interaction, such that dabigatran 110 mg twice a day compared with warfarin was associated with a lower risk of major bleeding in patients aged &lt;75 years (1.89% versus 3.04%; P &lt;0.001) and a similar risk in those aged ≥75 years (4.43% versus 4.37%; P =0.89; P for interaction &lt;0.001), whereas dabigatran 150 mg twice a day compared with warfarin was associated with a lower risk of major bleeding in those aged &lt;75 years (2.12% versus 3.04%; P &lt;0.001) and a trend toward higher risk of major bleeding in those aged ≥75 years (5.10% versus 4.37%; P =0.07; P for interaction &lt;0.001). The interaction with age was evident for extracranial bleeding, but not for intracranial bleeding, with the risk of the latter being consistently reduced with dabigatran compared with warfarin irrespective of age. Conclusions— In patients with atrial fibrillation at risk for stroke, both doses of dabigatran compared with warfarin have lower risks of both intracranial and extracranial bleeding in patients aged &lt;75 years. In those aged ≥75 years, intracranial bleeding risk is lower but extracranial bleeding risk is similar or higher with both doses of dabigatran compared with warfarin. Clinical Trial Registration— http://www.clinicaltrials.gov . Unique identifier: NCT00262600.

Risk of Bleeding With 2 Doses of Dabigatran Compared With Warfarin in Older and Younger Patients With Atrial Fibrillation