Comparison of Anti-Xa Levels in Obese and Non-Obese Pediatric Patients Receiving Treatment Doses of Enoxaparin

Abstract

To determine if using actual body weight to dose enoxaparin in obese pediatric patients results in higher anti-Xa levels compared with non-obese pediatric patients. This was a retrospective case-matched study of obese and non-obese pediatric patients receiving treatment doses of enoxaparin in a tertiary care children's hospital. Patients were included if they were initiated on treatment doses of enoxaparin, had appropriate anti-Xa levels drawn, and were between 2 and 18 years of age. Patients with renal insufficiency, hyperbilirubinemia, goal anti-Xa level <0.5 or >1 unit/mL, or receiving mechanical circulatory support were excluded. Obese patients who met study criteria were matched on a 1:1 basis with non-obese patients. All baseline characteristics were similar except for body mass index percentile (98.2 ± 2 vs 48.7 ± 15, P < .01). Obese patients had higher initial anti-Xa levels (0.67 ± 0.27 vs 0.53 ± 0.24 unit/mL, P = .028). Over time, obese patients required a lower mean dose to achieve therapeutic anti-Xa levels than non-obese patients (0.81 ± 0.19 vs 1.1 ± 0.4 mg/kg, P = .005). The mean initial anti-Xa level was higher in obese pediatric patients compared with non-obese pediatric patients, but a dosage adjustment was not required. Obese patients may need closer monitoring over time to avoid supratherapeutic levels and possible bleeding events.