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 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.