Studies among populations at high risk of venous thromboembolism (VTE) have demonstrated that recommended doses for enoxaparin thromboprophylaxis are associated with high incidence of subprophylactic anti-factor Xa (anti-Xa) levels. This study examines the efficacy and safety of dose-adjusted enoxaparin guided by anti-Xa levels.

Patients undergoing abdominal cancer operation had dose adjustments based on peak anti-Xa levels to attain a target of >0.20 IU/mL were prospectively enrolled and compared with a historic cohort of patients receiving recommended thromboprophylaxis. Incidence of in-hospital VTE and major bleeding after changes in enoxaparin dosing were monitored.

The study population comprised 197 patients—64 patients in the prospective intervention group and 133 patients in the control group. Baseline characteristic were similar between the intervention and control groups, with the exception of the Caprini score (8.09 vs 7.26; p = 0.013). In the intervention group, 50 of 64 patients (78.1%) initially had subprophylactic peak anti-Xa levels. The VTE rates were lower in the intervention group than the control group (0% vs 8.27%; p = 0.018). There were no differences in major bleeding events (3.12% vs 1.50%; p = 0.597), rates of postoperative packed RBC transfusion (17.2% vs 23.3%; p = 0.426), or mean Hgb on discharge (9.58 vs 9.37g/dL; p = 0.414). Therapeutic anti-Xa levels correlated positively with age (65.7 vs 58.2 years; p = 0.022) and correlated negatively with operating room time (203 vs 281 minutes; p = 0.032) and BMI (25.3 vs 29.2 kg/m²; p = 0.037).

Thromboprophylactic enoxaparin 40 mg daily is often associated with subprophylactic peak anti-Xa levels. Dose adjustment based on anti-Xa levels increased the daily enoxaparin dose, resulting in a lower rate of in-hospital VTE without increased risk of bleeding.