Prophylactic enoxaparin doses may be inadequate in patients undergoing abdominal cancer surgery

Background The incidence of venous thromboembolism has increased in patients following cancer surgery despite the increased use of prophylactic anticoagulants, suggesting standard doses may be inadequate. We sought to determine the adequacy of enoxaparin prophylaxis in patients undergoing abdominal cancer surgery. Methods Peak and trough anti-Xa levels were measured in patients receiving enoxaparin thromboprophylaxis (40 mg daily or 30 mg twice daily, at the surgeon's discretion) after undergoing open abdominal cancer surgery at a single institution. Results Fifty-five patients received enoxaparin 40 mg daily (group 1), 18 received 30 mg twice daily (group 2; total n = 73). There were no significant differences in gender, age, body mass index, creatinine clearance, diagnosis, or procedure between the two groups. Thirty-nine patients (53.4%) had inadequate peak anti-Xa levels (<0.2 IU/mL) and 69 patients (94.5%) had inadequate trough levels (≤0.1 IU/mL). Group 2 had lower mean peak levels (0.14 ± 0.02 IU/mL) than group 1 (0.22 ± 0.01, P = 0.003), and higher mean trough levels (0.06 ± 0.017) than group 1 (0.02 ± 0.004, P = 0.033). Group 2 had lower incidence of adequate peak anti-Xa levels than group 1 when adjusting for gender, age, body mass index, and preoperative creatinine clearance (OR 0.23, P = 0.039). Conclusions The majority of patients had inadequate anti-Xa levels following abdominal cancer surgery, calling into question standard prophylactic enoxaparin dosing.