Weight-Based Enoxaparin Dosing vs. Standard Dosing in Trauma Patients

Introduction

Thromboembolic disease is a common cause of morbidity and mortality in trauma patients. Without routine thromboprophylaxis, it is estimated to occur in up to 65% of these patients. Thromboprophylaxis is a routine part of care for trauma patients, most commonly using low-molecular-weight heparins, such as enoxaparin.

In the United States, trauma patients are commonly prescribed enoxaparin at a dose of 30 mg every 12 hours. Previous studies have highlighted that this dosing regimen is associated with sub-prophylactic levels of anti-Xa activity in a significant number of patients. Subsequent studies have adjusted the enoxaparin dose based on patient weight, resulting in an increased percentage of patients achieving effective prophylactic anti-Xa activity levels.

Furthermore, it was found that weight-based dosing should consider the patient's total body weight or body surface area, rather than BMI. This is important because adjustments should be made not only for obese patients but also for those with a normal BMI.

The aim of the clinical study presented below was to test the hypothesis that patients with weight-based dosing are more likely to achieve effective prophylactic anti-Xa levels compared to those on a standard dosing regimen.

Methodology and Study Progress

The study included patients aged ≥ 18 years who were admitted to a trauma center during a 6-month observation period. For the retrospective control group, patients receiving enoxaparin at the standard dose of 30 mg every 12 hours were included. In the prospective group, dosing was based on weight with an initial dose of 0.5 mg/kg every 12 hours.

In both groups, peak anti-Xa activity was measured 4 hours after administering the third dose of enoxaparin. An effective prophylactic anti-Xa range was defined as 0.2–0.5 IU/ml. For patients in the prospective group who did not achieve the target anti-Xa range after the first measurement, the dose of enoxaparin was adjusted by ±10 mg.

The primary goal of the study was to evaluate the proportion of patients achieving an effective anti-Xa range in both groups. Secondary objectives included finding correlations between anti-Xa activity and patients' physical characteristics.

Results

The study included a total of 84 patients (44 in the retrospective control group and 40 in the prospective experimental group). In both groups, the majority of cases involved blunt trauma (89 vs. 93%). The groups did not significantly differ in basic characteristics. Due to the low incidence of thromboembolic disease (2 vs. 1), this parameter could not be evaluated in relation to the achieved therapeutic anti-Xa range.

The average peak anti-Xa activity was significantly lower in the control group (0.26 ± 0.01) compared to the prospective group with initial weight-based dosing (0.32 ± 0.02; p = 0.009). The average peak anti-Xa activity was also significantly lower in the control group compared to the prospective group after dose adjustment following initial anti-Xa activity assessment (0.32 ± 0.02; p = 0.007).

Significantly more patients in the retrospective group had sub-prophylactic anti-Xa values compared to the prospective group (25 vs. 5%; p = 0.03). There was no significant difference in the overall prophylactic range between the groups due to patients with supraprophylactic anti-Xa values in the weight-based dosing group (25 vs. 12.5%; p = 0.173).

However, after adjusting the individual enoxaparin dose, no cases of anti-Xa activity outside the therapeutic range were observed in the prospective group (25% vs. 0%; RR ∞; p = 0.003). In the prospective group, 5 patients required further dose adjustments, with 3 reaching a supraprophylactic anti-Xa range and 2 reaching a sub-prophylactic anti-Xa range, after the initial weight-based dose.

No cases of bleeding were recorded in the study. In both groups, a correlation was observed between anti-Xa activity and body surface area and weight, but not BMI, confirming findings from previous clinical studies.

Conclusion

The results of the cited study indicate that weight-based dosing in trauma patients is more effective for achieving the desired anti-Xa activity than standard dosing regimens. Additionally, a correlation between anti-Xa activity and body surface area and weight, but not BMI, was confirmed.

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Source: Rodier S. G., Bukur M., Moore S. et al. 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. Eur J Trauma Emerg Surg 2021; 47 (1): 145–151, doi: 10.1007/s00068-019-01215-0.