Evaluation of Prophylactic Enoxaparin Anti-Xa Levels in Individuals Greater Than 150 kg

Introduction: Dosing prophylactic enoxaparin is challenging in Class III obesity. Most reports utilize either fixed or 0.5mg/kg weight-based dosing twice daily and include only a small portion of individuals >150kg. Our objective was to estimate an optimal weight-based prophylactic enoxaparin dose for ≥150kg individuals admitted to the Intensive Care Unit (ICU) or Progressive Care Unit (PCU).


Methods: This retrospective study included ≥150kg adult patients admitted to the ICU/PCU between January 1st, 2014–April 30th, 2024, who received twice daily prophylactic enoxaparin (goal peak anti-Xa 0.2-0.4IU/mL). At least one peak anti-Xa was required, obtained 3-5 hours after the 3rd consecutive dose. Those who were pregnant, incarcerated or had a creatinine clearance (CrCl) < 60mL/min were excluded. The primary outcome was the range of dosing that produced goal prophylactic peak anti-Xa following linear regression modeling. Secondary outcomes were hospital and ICU/PCU length of stay (LOS), in-hospital mortality, and VTE/bleed events within 72 hours after an eligible peak anti-Xa. Descriptive statistics included counts and percentages for categorical variables and median and IQR for continuous variables. SAS version 9.4 was used for analysis and a p-value < 0.05 was considered statistically significant.


Results: 72 encounters and 117 peak anti-Xa levels were assessed. Patients were 44 (39-54) years old, male (51.4%) and weighed 186kg (169.7-205.9) with a BMI of 63.4kg/m2 (56.2-71.6). At the time of peak anti-Xa collection, 68.4% were managed by medical teams and 31.6% by surgical, with 32.5% on mechanical ventilation. CrCl was 169.2mL/min (124.3-214.2) and patients received 4 doses (4-6) before peak anti-Xa, with a time between of 247 minutes (222-270). Linear regression modeling revealed a statistically significant correlation between weight-based dose and peak anti-Xa (p < 0.0001). The r2=0.28 and a dose between 0.23mg/kg-0.44mg/kg was predicted to achieve a peak anti-Xa of 0.2-0.4. Hospital LOS was 14 days (9-21.25), ICU/PCU LOS was 10 days (6.5-16), and only 2 patients (2.8%) died during hospitalization. No VTE or bleed events were observed.


Conclusions: Weight-based enoxaparin 0.23mg/kg-0.44mg/kg is expected to achieve a peak anti-Xa within prophylactic goal range (0.2-0.4) in ICU/PCU patients weighing ≥150kg.