Distribution of apixaban plasma concentrations across prescribed dose groups for ischemic stroke prevention in atrial fibrillation

Background Apixaban is an oral anticoagulant used to prevent ischemic stroke in patients with non-valvular atrial fibrillation. However, the effects of dose reduction criteria on apixaban plasma concentrations in Korean patients remains unclear. Methods We performed a single-center laboratory study to evaluate plasma concentrations of apixaban prescribed in real-world clinical practice. Blood specimens were collected from the patients without missing or changing doses before sampling. Plasma concentrations were measured using anti-factor Xa chromogenic assays based on heparin liquid-reagent technology. Results We studied 284 patients across four prescribed-dose groups: standard dose (n = 204), on-label reduced dose (n = 47), off-label underdose (n = 29), and off-label overdose (n = 4). Peak and trough concentrations were higher in the standard group than the off-label underdose group. The proportion of apixaban’s peak concentrations within the expected 5th–95th percentile distribution range was higher in the off-label underdose group than the standard group (96.0 vs 77.8%, p = 0.023). Among patients receiving standard and on-label reduced dose, despite guideline-concordant prescribing, a substantial proportion of those aged ≥ 60 years, with body weight ≤ 80 kg, or with creatinine clearance 30–80 mL/min exhibited peak apixaban concentrations exceeding the upper limit of the expected reference range. Conclusions In Korean patients with atrial fibrillation, a subset receiving the standard or on-label reduced dose exhibited higher peak concentrations exceeding the upper limit of the expected ranges. Whereas, concentrations in the off-label underdose group, predominantly remained within the expected range.