Determination of Optimal Weight-Based Enoxaparin Dosing and Associated Clinical Factors for Achieving Therapeutic Anti-Xa Assays for Deep Venous Thrombosis Prophylaxis.

BACKGROUND: Previous studies have evaluated dose-to-weight ratios to define best practices for obtaining therapeutic anti-Xa assays for enoxaparin venous thromboembolism (VTE) prophylaxis. These studies have not examined relationships among dosing, patient characteristics, and therapeutic assays. This study examines factors associated with therapeutic assays and enoxaparin prophylaxis.

STUDY DESIGN: This is a retrospective review of patients admitted to a Level 1 trauma center between March 2016 and June 2018. Prophylaxis was managed according to the trauma service's enoxaparin VTE prophylaxis protocol, which targets anti-Xa concentrations of 0.2 to 0.5 IU/mL. Assays were divided into sub-therapeutic, therapeutic, and super-therapeutic groups to determine factors associated with therapeutic concentrations.

RESULTS: Overall, 623 patients (634 total anti-Xa assays) were identified during the study period. Patients with sub-therapeutic (n = 35) and therapeutic (n = 536) assays did not differ. Significant differences were identified between patients with therapeutic and super-therapeutic assays (n = 63). Receiver operating characteristic curve analysis was used to determine that the optimal cutoff for the dose-to-weight ratio was 0.4 mg/kg/dose (area under the curve 0.78; 95% CI 0.73 to 0.84; p < 0.001) differentiating therapeutic and super-therapeutic assays. Logistic regression revealed male sex, doses of 0.31 to 0.4 mg/kg, and creatinine clearance > 90 mL/min were independently associated with therapeutic assays. The combined effect of these 3 variables showed that therapeutic assays were 13.76 times more likely to occur (OR 13.76; 95% CI 3.43 to 56.96; p < 0.001).

CONCLUSIONS: These data demonstrate that a dose of 0.4 mg/kg predicts a therapeutic anti-Xa level. When regimens of 0.31 to 0.4 mg/kg/dose are administered in males with a creatinine clearance >90 mL/min therapeutic results are 13.76 times more likely, suggesting that monitoring with anti-Xa assays might be unnecessary in this subgroup. Additional prospective study of these findings is warranted.