Prophylactic Enoxaparin Dosing and Anti-Xa Levels in Medicine Patients With Obesity

Introduction: Previous studies have shown that the manufacturer's standard fixed dosing of enoxaparin for venous thromboembolism (VTE) prophylaxis leads to sub-prophylactic anti-Xa levels in medicine patients with obesity. Yet, there is limited literature describing higher dosing strategies in this patient population, and an optimal dosing regimen has not been well-established. Objective: The primary objective was to evaluate mean doses (mg/kg/d) of prophylactic enoxaparin that are associated with goal anti-Xa levels in medicine patients with obesity across 3 body mass index (BMI) groups (40-49 kg/m², 50-59 kg/m², ≥60 kg/m²). Methods: This is a single-center, retrospective cohort study of adult patients (age ≥18 years) with BMI ≥40 kg/m² admitted to a medicine team with at least 1 appropriately drawn anti-Xa level between January 2018 and July 2023. The institution's goal anti-Xa level for VTE prophylaxis was 0.2 to 0.4 units/mL. The primary outcome was the comparison of mean dose between those within anti-Xa at goal and not at goal. Secondary outcomes included the percentages of initial anti-Xa levels below, within, or above goal range and the incidence of new VTE and major bleeding events during hospitalization while on enoxaparin. All outcomes were stratified into 3 BMI groups: 40-49 kg/m², 50-59 kg/m², and ≥60 kg/m². Results: Median dose of those with final anti-Xa level at goal was significantly higher than that of those not in goal anti-Xa range across all 3 BMI groups (0.57 vs 0.50 mg/kg/d; P < 0.05). The majority of the initial anti-Xa levels were subprophylactic, with only 35.7% of patients (or 75 of 210 patients) had initial anti-Xa within the goal range. There were no statistically significant differences in the number of blood transfusions or VTE events between the groups. Conclusion: Findings suggest that medicine patients with BMI ≥40 kg/m² may require enoxaparin doses higher than 0.5 mg/kg/d to reach goal prophylactic anti-Xa level. However, more robust data are necessary to further validate these results and the clinical implications.