Evaluation and Pharmacokinetics of Treatment Dose Enoxaparin in Hospitalized Patients with Morbid Obesity

Background: The pharmacokinetic properties of enoxaparin may lead to supratherapeutic antifactor Xa (anti-Xa) levels and increased bleeding when standard treatment doses are used in patients with morbid obesity. Objective: To evaluate the dose of enoxaparin needed to achieve therapeutic anti-Xa levels in a prospective, masked observational cohort of heterogeneous inpatients with morbid obesity and to determine whether patients with morbid obesity treated with 1 mg/kg of enoxaparin are at increased risk of supratherapeutic levels and bleeding events compared to patients receiving lower doses. Methods: Hospitalized patients with a body mass index ≥40 kg/m² or actual body weight ≥140 kg and prescribed treatment doses of enoxaparin <60 mg per day were enrolled and consented to phlebotomy for determination of anti-Xa levels. Results: Forty-one patients were included for data analysis. The dose of enoxaparin that resulted in therapeutic and supratherapeutic anti-Xa levels at steady state was 0.83 mg/kg and 0.98 mg/kg (-0.11; 95% confidence interval [CI] -0.20 to-0.01, P .02), respectively. Enoxaparin dose as mg/kg of actual body weight was an independent predictor of having a supratherapeutic anti-Xa level. Patients with doses ≤0.95 mg/kg versus ≥0.95 mg/kg were less likely to have supratherapeutic levels (odds ratio 0.21 [95% CI 0.05-0.84], P .02) and had similar rates of subtherapeutic levels. Doses ≤0.95 mg/kg and ≥0.95 mg/kg resulted in similar bleeding rates of 17.9% and 22.2% (P .71), respectively. Conclusion: Patients with morbid obesity required less than the recommended 1 mg/kg enoxaparin dose to achieve therapeutic peak anti-Xa levels; therefore, initiation with lower dosages is prudent and anti-Xa monitoring should guide dosage adjustments.