Clinical and Pharmacological Effects of Apixaban Dose Adjustment in the ARISTOTLE Trial

BACKGROUND In the ARISTOTLE (Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation) trial, patients with atrial fibrillation and >= 2 dose-adjustment criteria (age >= 80 years, weight <= 60 kg, or creatinine >= 1.5 mg/dl [133 mu mol/l]) were randomized to receive apixaban 2.5 mg twice daily or warfarin. OBJECTIVES The purpose of this study was to describe the effects of apixaban dose adjustment on clinical and pharmacological outcomes. METHODS Patients receiving the correct dose of study drug were included (n = 18,073). The effect of apixaban 2.5 mg twice daily versus warfarin on population pharmacokinetics, D-dimer, prothrombin fragment 1 + 2 (PF1+2), and clinical outcomes was compared with the standard dose (5 mg twice daily). RESULTS Patients receiving apixaban 2.5 mg twice daily exhibited lower apixaban exposure (median area under the concentration time curve at a steady state 2,720 ng/ml vs. 3,599 ng/ml; p < 0.0001) than those receiving the standard dose. In patients with >= 2 dose-adjustment criteria, reductions in D-dimers (p interaction = 0.20) and PF1+2 (p interaction = 0.55) were consistent with those observed in the standard-dose population. Patients with >= 2 dose-adjustment criteria (n = 751) were at higher risk for stroke/systemic embolism, major bleeding, and all-cause death than the standard-dose population (0 or 1 dose-adjustment criterion, n = 17,322). The effect of apixaban 2.5 mg twice daily versus warfarin in the >= 2 dose-adjustment criteria population was consistent with the standard dose in the reductions in stroke or systemic embolism (p interaction = 0.26), major bleeding (p interaction = 0.25), and death (p interaction = 0.72). CONCLUSIONS Apixaban drug concentrations were lower in patients receiving 2.5 mg twice daily compared with 5 mg twice daily. However, the effects of apixaban dose adjustment to 2.5 mg versus warfarin were consistent for coagulation biomarkers and clinical outcomes, providing reassuring data on efficacy and safety. (Apixaban for the Prevention of Stroke in Subjects With Atrial Fibrillation [ARISTOTLE]; NCT00412984).