Anti-Factor Xa Activity of Prophylactic Enoxaparin Regimens in Critically Ill Patients

Background: Enoxaparin is frequently used as prophylaxis for deep venous thrombosis in critically ill patients. Objectives: To evaluate three enoxaparin prophylactic regimens in critical care patients with and without administration of a vasopressor. Methods: Patients admitted to intensive care units (general and post-cardiothoratic surgery) without renal failure received, once daily, a subcutaneous fixed dose of 40 mg enoxaparin, a subcutaneous dose of 0.5 mg/kg enoxaparin, or an intravenous dose of 0.5 mg/kg enoxaparin. Over 5 days anti-activated factor X levels were collected before the daily administration and 4 hours after the injection. Results: Overall, 16 patients received the subcutaneous fixed dose, 15 received the subcutaneous weight-based dosage, and 8 received the dose intravenously. Around two-fifths (38%) of the patients received vasopressors. There was no difference between anti-activated factor X levels regarding vasopressor administration. However, in all three groups the levels were outside the recommended range of 0.1 IU/ml and 0.3 IU/ml. Conclusions: Although not influenced by vasopressor administration, the enoxaparin regimens resulted in blood activity levels outside the recommended range.