Apixaban in low‐weight patients with cancer‐associated thrombosis: A cross sectional study of drug levels

Apixaban, a direct factor Xa inhibitor, has been shown to be at least as safe and probably more effective than dalteparin for the treatment of cancer‐associated thrombosis (CAT) as reported in the ADAM‐VTE and Caravaggio studies, which included a low percentage of underweight patients. Lower‐weight–based dosing is supported by cancer‐specific studies such as half‐dose edoxaban in the Hokusai‐VTE cancer trial in individuals weighing <60 kg. Objective To examine apixaban plasma trough levels in low‐weight individuals with CAT, stably anticoagulated with full or half‐dose apixaban. Methods This was a cross‐sectional study of 61 routinely treated patients with active cancer and venous thromboembolism comparing three groups: patients weighing >60 kg treated with apixaban 5 mg twice daily, patients weighing ≤60 kg also receiving apixaban 5 mg twice daily, and patients weighing ≤60 kg given half‐dose apixaban (2.5 mg twice daily). Apixaban plasma steady‐state trough levels were determined on a single occasion. Results Mean apixaban plasma trough levels were similar for patients weighing >60 kg on full‐dose apixaban to those weighing ≤60 kg taking 2.5 mg twice daily (mean, 109 ng/dL; 95% confidence interval [CI], 74‐145; standard deviation [SD]: 77.6; and mean,101 ng/dL, 95% CI, 67‐135; SD: 80, respectively). Mean values for low‐weight patients (≤60 kg) on the full 5 mg twice‐daily dosing tended to be higher (mean, 136 ng/dL; 95%CI, 70‐201; SD:114), without statistical significance ( P  = .22). Conclusions This study supports the rationale for studying weight‐based adjustments in apixaban dosing in prospective studies evaluating safety and efficacy of dose reduction in low‐weight patients with cancer.