Apixaban Concentrations in Routine Clinical Care of Older Adults With Nonvalvular Atrial Fibrillation

Direct-acting oral anticoagulants are first-line agents for prevention of stroke in patients with nonvalvular atrial fibrillation (NVAF), but data are limited for the oldest patients, and with reduced dosing. To determine steady-state apixaban peak and trough concentrations during routine care of older adults with NVAF, compare concentrations to clinical trial concentrations, and explore factors associated with concentrations. A cross-sectional study of medically stable older adults with NVAF (≥75 years or ≥70 years if Black) receiving apixaban. Peak (2-4.4 hours post-dose) and trough (before next dose) concentrations were determined by anti-Xa activity calibrated chromogenic assay. Patient characteristics associated with concentrations were determined by multivariate modeling. The median age of patients (n = 115) was 80 (interquartile range: 77-84) years. The cohort comprised 46 women and 69 men; of which 98 are White, 11 Black, and 6 Asian. With 5 mg twice daily per labelling (n = 88), peak concentrations were higher in women: 248 ± 105 vs 174 ± 67 ng/mL in men ( < 0.001) and exceeded expected 95% range in 6 of 30 vs 0 of 55 men ( = 0.002). With 2.5 mg twice daily per label (n = 11), concentrations were