Background: Low-molecular-weight heparin is effective for prevention of venous thromboembolism. The efficacy of daily dosing in critically ill patients is unknown.
Methods: Seventeen critically ill patients on 40 mg of enoxaparin subcutaneously daily were studied. Anti-Xa activity was measured 4 hours after the third dose and before the fourth dose. Adverse events were recorded.
Results: Mean peak anti-Xa activity was 0.19 +/- 0.09 International Units/mL and mean trough was 0.044 +/- 0.04 International Units/mL. The recommended target range is 0.1 to 0.2 International Units/mL. The trough was below therapeutic levels in all but two patients. One thrombosis occurred in a patient despite a therapeutic trough.
Conclusion: Daily dosing of enoxaparin is inadequate for critically ill patients and should be abandoned. Further studies using twice daily dosing are needed. Patients with renal insufficiency may require an increased interval of administration (daily dosing). Anti-Xa levels may not correlate with the risk of thromboembolic complications. Patients with renal insufficiency and morbid obesity may require alternative dosing and monitoring of anti-Xa levels.