Assessment of anti-factor Xa activity of enoxaparin for venous thromboembolism prophylaxis in morbidly obese surgical patients

BACKGROUND Venous thromboembolism (VTE) can be encountered by 60% of hospitalized patients. Anticoagulants have been recommended to reduce the risk of VTE in patients with risk factors. However, no specific dosing recommendations for obese patients are provided in the current practice guidelines. The purpose of this study was to determine the efficacy and safety of weight-based dosing of enoxaparin for VTE prophylaxis among morbidly obese patients undergoing surgery. METHODS Adult patients were enrolled if they have a body mass index (BMI) of ≥35 kg/m2 and were scheduled for surgery. These patients were prescribed enoxaparin (0.5 mg/kg subcutaneously [SC] once daily). Peak anti-factor Xa levels were measured 4 h after the third dose of enoxaparin. The primary outcome measure was to determine whether a weight-based dosing of enoxaparin of 0.5 mg/kg produce the anticipated peak anti-Xa levels (0.2-0.6 IU/m) among obese patients undergoing surgery. Secondary outcomes include the incidence of VTE, the incidence of minor or major bleeding, and the incidence of heparin-induced thrombocytopenia (HIT). RESULTS Fifty patients were enrolled in the study. The mean age was 53 ± 16 years, 74% of the patients were female. The mean BMI was 40.5 ± 5, and the average enoxaparin dose was 50 ± 9.8 SC daily. Nearly 88% of the patients reached the target anti-factor Xa (0.427 ± 0.17). None of the patients developed HIT or VTE. There was no incidence of major or minor bleeding. CONCLUSIONS Weight-based enoxaparin dose led to the anticipated peak anti-Xa levels (0.2-0.6 IU/mL) in most of the morbidly obese study patients undergoing surgery without any evidence of major side effects. The weight-based dosing of enoxaparin was also effective in preventing VTE in all patients. Although these results are promising, further comparative trials are needed in the setting of morbidly obese surgical patients.