2025 Southeastern Residency Conference

Title: Evaluation of Enoxaparin Dosing for Venous Thromboembolism Prophylaxis in Low Body Weight Non-Critically Ill Patients


Authors: Andrew Stewart, Alisha B. Terry, Eric Shaw


Background: Enoxaparin is an anticoagulant used for venous thromboembolism (VTE) prophylaxis and treatment. Standard dosing for VTE prophylaxis in adult medical patients is 40 mg daily. There is currently guidance for the dosing of enoxaparin for obese patients with a BMI ≥40 kg/m² but there is minimal guidance for patients with low body weight who are not in the intensive care unit. This study aims to assess the safety and efficacy of reduced dosing strategies for low body weight patients under 50 kg. A retrospective study by Yam et al. found that enoxaparin 30 mg daily achieved target anti-Xa levels in about 74% of low-weight patients without significantly increasing bleeding risk. Other studies, including those by Nemeth et al., Barba et al., and Dybdahl et al., reported no significant difference in bleeding risk between standard and reduced dosing. However, Buckheit et al. and Cappetto et al. found reduced doses were associated with fewer bleeding events. This study compared dosing strategies, evaluated anti-Xa levels, and assessed bleeding and thrombotic events to determine the optimal approach for low body weight, non-critically ill patients.


Methods: This was a retrospective cohort study that was conducted from January 1, 2020, to August 30, 2024, at a 711-bed hospital. It included adult patients, weighing ≤50 kg, who received enoxaparin for VTE prophylaxis for at least 3 days, and had anti-Xa levels measured 3-5 hours after at least the third consecutive dose. Exclusion criteria included patients presenting with a bleed or thrombi, those on anticoagulation on admission, creatinine clearance <30 mL/min, admitted to the ICU, on an orthopedic or trauma service, received an alternative dose of enoxaparin for ≥2 days unless indicated by anti-Xa, did not receive VTE prophylaxis for 48 hours after admission, and pregnant or incarcerated patients. The study compared enoxaparin 20 mg daily vs. 30 mg daily for VTE prophylaxis. The primary outcome was the percentage of patients achieving target anti-Xa levels (0.2-0.4 IU/mL). Secondary outcomes included bleeding (gastrointestinal, genitourinary, hemoptysis, epistaxis, and surgical sites bleeds) and thrombotic events (VTE, pulmonary embolism). 


Results: Of the 1368 patients that were screened, 54 patients were included in the final analysis. Forty-four patients received enoxaparin 30 mg daily and 10 patients received enoxaparin 20 mg daily for VTE prophylaxis. For the primary outcome, the mean anti-Xa level was 0.30 (±0.13) for the 30 mg group and 0.17 (±0.09) for the 20 mg group. The number of patients whose anti-Xa level was in goal for the 30 mg group was 33 (75%) and the number for the 20 mg group was 3 (30%). For the secondary outcomes neither group had a clotting event but the 30 mg group had 2 bleeding events.


Conclusion: This study found that 20 mg of enoxaparin daily for VTE prophylaxis does not on average provide therapeutic anti-Xa levels for non-critically ill adult patients that weigh less than 50 kg. Enoxaparin 30 mg daily for VTE prophylaxis does on average provide therapeutic anti-Xa levels for the specified patient population. Enoxaparin 30 mg daily had more bleeding events compared to 20 mg daily. Therefore, based on this study, non-critically ill adult patients that weigh less than 50 kg should be started on enoxaparin 30 mg daily for VTE prophylaxis because this will result in more therapeutic anti-Xa levels.