Enoxaparin is commonly used to prevent venous thromboembolism (VTE) [1, 2] but has not been well-studied in patients with extreme obesity, a population at high risk for VTE. We prospectively compared three enoxaparin dosing regimens for the achievement of goal peak anti-Factor Xa levels in medically-ill patients (n=31) with extreme obesity (body mass index (BMI) ≥ 40 kg/m2). Patients were assigned to receive fixed-dose (FD) enoxaparin 40mg daily (QDay, n=11), weight-based, lower-dose (LD) enoxaparin 0.4 mg/kg QDay (n=9), or weight-based, higher-dose (HD) enoxaparin 0.5 mg/kg QDay(n=11). The average BMI and weight of the entire cohort was 62.1 kg/m2 (range 40.5-82.4) and 176 kg (range 115-256 kg) and did not differ between groups. Peak anti-Factor Xa levels were significantly higher in the HD group compared to either LD or FD groups. Patients in the HD group achieved target anti-Factor Xa levels more frequently than the LD and FD groups (p<0.05). Peak anti-Factor Xa levels did not correlate with age, weight, BMI, or creatinine clearance, demonstrating the predictability of weight-based enoxaparin dosing. There were no adverse events (e.g. bleeding, thrombosis, thrombocytopenia). To our knowledge, this is the first prospective comparative study demonstrating that in extremely obese, medically-ill patients enoxaparin 0.5 mg/kg QDay is superior to fixed-dose and lower-dose enoxaparin for the achievement of target anti-Factor Xa levels.

Long-standing controversy has surrounded aspirin as an antithrombotic modality to prevent venous thromboembolism (VTE), particularly in the orthopedic surgery arena. New data are emerging on the use of aspirin for both primary VTE prevention and secondary prevention of recurrent VTE after an initial anticoagulation course. This review article will provide the history behind the controversy, information regarding recent or ongoing clinical trials of aspirin for primary VTE prevention in major orthopedic surgery, evidence for aspirin in secondary prevention of recurrent VTE, and suggestions for future research. Aspirin may be a reasonable option for VTE prevention in certain major orthopedic surgery patients. Additionally, investigation among non-orthopedic populations such as the acutely ill medical patient and the non-orthopedic surgery patient is encouraged to provide further safety and efficacy data.