Venous Thromboembolism Prophylaxis with Enoxaparin Versus Unfractionated Heparin in Patients with Low Body Weight

Background Although reduced doses of enoxaparin have been studied in low body weight patients, no study has directly compared enoxaparin to unfractionated heparin for venous thromboembolism (VTE) prophylaxis in this population. Objective To determine the most safe and efficacious parenteral venous thromboembolism prophylaxis regimen for low body weight patients. Design Retrospective cohort. Methods Hospitalized patients weighing < 55 kg receiving either enoxaparin or unfractionated heparin for VTE prophylaxis over a period of two and a half years were evaluated. Primary outcomes included rates of VTE and overall bleeding events. Secondary outcomes included rates of major and clinically relevant minor bleeding. Dosing regimens were analyzed to determine associations between dose, weight, creatinine clearance, VTE, and bleeding events. Primary and secondary outcomes were evaluated using Chi squared and Fischer's Exact tests. Results Three hundred and sixty-one patients contributed 400 episodes of VTE prophylaxis. Most patients were female (88%), had a Padua score ≥ 4 (82%) and were admitted to medical/surgical units (76%). VTE rates were 0.4% in patients receiving enoxaparin and 2.5% in patients receiving unfractionated heparin ( P = 0.334). Bleeding rates were 12% and 11% in the enoxaparin and unfractionated heparin groups, respectively ( P = 1). Patients receiving enoxaparin 30 mg daily had bleeding rates of 7.6% compared to 14.7% in patients receiving 40 mg daily ( P = 0.134). Patients receiving heparin twice daily had no bleeding events compared to 12.9% of patients receiving heparin three times daily ( P = 0.222). Conclusion Overall, no difference in VTE or bleeding rates were found between patients weighing < 55 kg receiving enoxaparin versus unfractionated heparin, and there was no difference in bleeding or VTE events in the patients receiving enoxaparin 30 mg daily. Due to this, empirically reducing the dose of enoxaparin for VTE prophylaxis appears reasonable and safe in patients weighing < 55 kg.