Weight-based enoxaparin with anti-factor Xa assay-based dose adjustment for venous thromboembolic event prophylaxis in adult trauma patients results in improved prophylactic range targeting.

Background: Venous thromboembolism (VTE) is a common morbidity in trauma patients. Standard VTE chemoprophylaxis is often inadequate. We hypothesized that weight-based dosing would result in appropriate prophylaxis more reliably than fixed dosing.
Methods: All patients admitted to a Level 1 trauma center over a 6-month period were included unless contra-indications for VTE prophylaxis existed. A prospective adjusted-dosing group was compared to a retrospective uniform-dosing group. The adjusted-dosing approach consisted of initial weight-based dosing of 0.5 mg/kg subcutaneously (subQ) every 12 h (q12h). Peak anti-factor Xa was measured. Patients outside of the prophylactic range had their dose adjusted by ± 10 mg. The uniform-dosing group received 30 mg subQ q12h, without adjustments.
Results: Eighty-four patients were included: 44 in the retrospective control cohort and 40 in the prospective experimental cohort. More patients were sub-prophylactically dosed in the uniform-dosing group relative to the adjusted-dosing group (25% vs 5%, p = 0.03). There was no difference in overall prophylactic range targeting, because the supra-prophylactically dosed patients in the adjusted-dosing group eliminated the effect (p = 0.173). However, after a single dose adjustment, zero patients were outside of prophylactic range (25% versus 0%, RR = infinite, p = 0.003). In the uniform-dosing group, anti-Xa level correlated with body surface area (BSA; R ²  = 0.33, p < 0.0001) and weight (R ²  = 0.26, p = 0.0005). Weight-based dosing both pre- and post-readjustment normalized the correlation of anti-Xa with BSA (R ²  = 0.07, p = 0.1) and weight (R ²  = 0.07, p = 0.1).
Conclusions: Weight-based VTE prophylaxis with anti-Xa-based dose adjustment improves prophylactic range targeting relative to uniform dosing and eliminates variances secondary to BSA and weight in trauma patients.