Utility of anti-factor Xa monitoring in surgical patients receiving prophylactic doses of enoxaparin for venous thromboembolism prophylaxis.

BACKGROUND: Between 2% and 10% of the highest risk surgery, patients have a "breakthrough" venous thromboembolism (VTE) event despite receipt of chemoprophylaxis. The goals of this review are to summarize how patient-level factors may predict enoxaparin metabolism and how alterations in enoxaparin dose magnitude and frequency affect both anti-factor Xa (aFXa) levels and downstream VTE events.

DATA SOURCES: Relevant articles were identified on PubMed. Fixed-dose prophylaxis provides inadequate enoxaparin prophylaxis for most surgical patients based on anti-factor Xa levels. Inadequate enoxaparin dosing has been correlated with both asymptomatic and symptomatic VTE events. Patient-level factors such as gross weight and extent of injury predict enoxaparin metabolism. Weight-based or weight-tiered dosing regimens-and real-time dose adjustment based on anti-factor Xa levels-allow an increased proportion of patients to have in-range anti-factor Xa levels.

CONCLUSIONS: Inadequate enoxaparin dosing may explain why some patients have VTE despite enoxaparin prophylaxis. Ongoing research in the utility of weight-based or anti-factor Xa level driven enoxaparin dosing and dose adjustment is reasonable.