Apixaban Levels in Octogenarian Patients with Non-valvular Atrial Fibrillation.

Background: There is a paucity of data on apixaban levels among octogenarians with non-valvular atrial fibrillation (NVAF). We aimed to compare apixaban levels between octogenarians (with and without dose reduction) and younger patients, to assess the frequency of high and above-range drug levels.

Methods: A cross-sectional, prospective study of 80 patients treated with apixaban for NVAF was conducted. Apixaban levels were compared among octogenarians treated with 5 mg twice daily (bid), octogenarians with appropriately reduced dose (2.5 mg bid), octogenarians with inappropriately reduced dose and younger patients (age < 70 years). Trough and peak levels were measured by a chromogenic assay calibrated for apixaban and compared to predicted manufacturer levels.

Results: A significant proportion of the cohort had above-range trough [n = 11 (13.8%)] and peak [n = 16 (20%)] levels, especially octogenarians with the 5-mg bid dosage [n = 6 (30%) for trough and n = 8 (40%) for peak]. No significant differences were found in the trough or peak geometric mean (GM) levels among the groups, apart from the peak GM levels between the 5-mg octogenarian group and the other two 2.5-mg bid octogenarian groups (p = 0.0004). The frequency of apixaban peak levels within the upper quartile was significantly higher in the 5-mg octogenarian group compared to the other groups [n = 12 (60%) of measurements, p = 0.019), whereas trough levels were comparable between groups.

Conclusion: High and above-range peak apixaban steady-state levels are highly prevalent in octogenarians receiving the appropriate dosage of 5 mg bid for NVAF stroke prevention. Age above 80 strongly affects apixaban levels.

Trial Registration: ClinicalTrials.gov Identifier number NCT02623049.