Finding individualised treatment in obese needing enoxaparin (FIT ONE): a multicentre study of therapeutic enoxaparin and the role of anti-factor Xa monitoring

Enoxaparin is dosed according to actual body weight in treatment of arterial and venous thrombosis. Due to its hydrophilic nature, it distributes according to lean body mass which may be problematic when dosing obese patients as this may increase the risk of bleeding events in this population. The aim was to evaluate current therapeutic enoxaparin dosing strategies, including Antifactor Xa (AFXa) level monitoring, in obese patients and to identify factors that contribute to treatment failure and excess anticoagulation. A retrospective cohort study was conducted reviewing patients administered therapeutic enoxaparin between May 2020 and April 2021. Data were collected on patient characteristics, enoxaparin therapy, AFXa monitoring, and outcomes. Regression models were constructed to assess variables of interest to estimate any association with AFXa levels. In total 762 patients were included in the analysis. The mean initial weight-based dose was 0.95 mg/kg twice daily (SD: +/- 0.12, IQR 0.92-1.01) and 1.04 mg/kg once daily (SD: +/- 0.26, IQR 0.93-1.12) and 14.4% of patients had AFXa monitoring. Treatment failure was experienced by 2.2%, 5% experienced bleeding. There was no association between the mean actual milligram per kilogram weight-based twice daily doses and subtherapeutic, therapeutic and supratherapeutic AFXa levels (P = 0.135). Obesity was not included in the final regression models due to lack of significance. At a mean therapeutic enoxaparin dose of 0.95 mg/kg twice daily and 1.04 mg/kg once daily no excess in treatment failure or bleeding events were observed in obese patients compared to the product information. Obesity was not an independent variable that affected the achievement of target AFXa levels.