Evaluation of weight based enoxaparin dosing on anti-Xa concentrations in patients with obesity

Current treatment dose of enoxaparin is based on total body weight (TBW), however dosage in obesity remains unclear. "Dose capping" commonly occurs if TBW > 100 kg minimising bleeding risk. However, this may result in under-dosing and increasing embolisation risk. The primary objective evaluated efficacy of current dosing strategies in obese patients and determined if resultant anti-Xa concentrations (aXaC) were therapeutic. The secondary objective was to investigate if an uncapped 0.75-0.85 mg/kg (TBW) twice daily dose, advocated by previous authors, results in therapeutic aXaC (0.5-1.0 IU/ml). This retrospective study included 133 patients with a median TBW of 128 kg, producing 59% therapeutic, 15% sub-therapeutic and 26% supra-therapeutic aXaC. Approximately 60% of patients in each dose group (< 0.75, 0.75-0.85 and > 0.85 mg/kg) had a therapeutic aXaC, however the percentage of sub-therapeutic versus supra-therapeutic was higher in the < 0.75 (27% vs 9%) and > 0.85 mg/kg (10% vs 34%) groups respectively. Most patients who weighed 100-119 kg (TBW) received doses > 0.85 mg/kg, however 32% had toxic aXaC. Those between 120 and 139 kg (TBW) had a high percentage of therapeutic aXaC (87%) when dosed < 0.75 mg/kg and a high percentage of supra-therapeutic aXaC (71%) when dosed > 0.85 mg/kg; although numbers were low. Dose reduction occurred in patients > 140 kg (TBW), however < 0.75 mg/kg resulted in higher percentage of sub-therapeutic aXaC (42%). Dosing at 0.75-0.85 mg/kg results in 62% of therapeutic, 14% sub-therapeutic and 24% supra-therapeutic aXaC. This appears to be a "safe" starting dose-range, however all obese patients should have aXaC monitoring due to high inter-patient variability.