Assessment of enoxaparin thromboprophylaxis dosing and anti-factor Xa levels in low-weight patients

Introduction: Centers of Medicare and Medicaid Services and The Joint Commission have set standards for reimbursement for Medicare-covered inpatient services, including venous thromboembolism (VTE) prophylaxis. For hospitalized patients at increased risk for thrombosis, pharmacologic thromboprophylaxis with anticoagulants is recommended. Fixed prophylactic doses of enoxaparin in low-weight patients may pose an increased risk of bleeding and prolonged hospitalization. Measured anti-factor Xa levels and observed bleeding events may be used to monitor the safety and efficacy of enoxaparin. Few articles have published the relationship between anti-factor Xa levels and body weight in low-weight patients.

Objectives:  This study will evaluate anti-factor Xa levels in low-weight patients receiving enoxaparin for VTE prophylaxis. More specifically, we will determine what factors are associated with anti-factor Xa levels and measure the extent to which body mass index affects anti-factor Xa levels.

Study Design: Retrospective chart review

Methods: Data is currently being collected from electronic medical records of patients admitted to any Loma Linda University Health inpatient facility between January 1, 2008 through August 24, 2015. We anticipate complete data analysis by March 2016.

Results: To date, six patients have been included in this study. These patients have a mean age of 29.7 years, mean weight of 42.5 kg, and mean BMI of 17.0 kg/m². One patient received enoxaparin 40 mg once daily, four patients received enoxaparin 30 mg once daily, and one patient received enoxaparin 30 mg twice daily. Therapeutic anti-factor Xa levels (pre-specified as 0.2 – 0.5 units/mL) were observed in 67% of patients and supratherapeutic anti-factor Xa levels were observed in 33% of patients. The mean anti-factor Xa level was 0.42 units/mL.

Conclusions:  Data collection is in progress. Presentation of the results of this study will provide clinicians with additional information on how to efficaciously and safely dose enoxaparin for VTE prophylaxis in low-weight patients.