Enoxaparin and Antifactor Xa Levels in Acute Burn Patients

Altered pharmacokinetics in critically ill patients have been shown to result in inadequate enoxaparin dosing for venous thromboembolism (VTE) prophylaxis. In the burn unit, routine monitoring of antifactor Xa levels was implemented to ensure adequate VTE prophylaxis. The purpose of this study was to examine the appropriateness of enoxaparin dosing for VTE prophylaxis in this specialized patient population. The authors reviewed patients with acute burn injury from June 1, 2009, to October 20, 2009, who had enoxaparin therapy monitored with antifactor Xa levels. Data collection occurred prospectively. Thirty-eight patients received enoxaparin subcutaneously for prophylaxis of VTE and had antifactor Xa levels measured. Thirty (79%) patients had initial antifactor Xa levels less than 0.2 U/ml. Enoxaparin dosages were subsequently increased as needed to achieve antifactor Xa levels of 0.2 to 0.4 U/ml. Eight of 38 patients never achieved goal antifactor Xa level before enoxaparin was discontinued. The median final dose required to achieve an antifactor Xa level within therapeutic range was 50 mg every 12 hours (range 30-70 mg). In linear regression, final enoxaparin dose correlated with TBSA. Two patients had clinically significant thromboembolic events. There were no documented episodes of significant hemorrhage, thrombocytopenia, or heparin-associated allergy. The low antifactor Xa levels observed in this study demonstrate that standard dosing of enoxaparin for VTE prophylaxis is inadequate for patients with acute burns. In these patients, both a higher initial enoxaparin dose and routine monitoring of antifactor Xa levels are recommended.