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Population Pharmacokinetics of Enoxaparin in Pediatric Patients

Background: There are no studies evaluating the pharmacokinetics of enoxaparin in the hospitalized pediatric patient population. Objective: To characterize the pharmacokinetics of enoxaparin in pediatric patients. Methods: A retrospective review of inpatients 1 to 18 years of age admitted to our institution who received enoxaparin with anti–factor Xa activity level monitoring was performed. Demographic variables, enoxaparin dosing, and anti–factor Xa activity levels were collected. Population pharmacokinetic analysis was performed with bootstrap analysis. Simulation (n = 10 000) was performed to determine the percentage who achieved targeted anti-Xa levels at various doses. Results: A total of 853 patients (male 52.1%, median age = 12.2 years; interquartile range [IQR] = 4.6-15.8 years) received a mean enoxaparin dose of 0.86 ± 0.31 mg/kg/dose. A median of 3 (IQR = 1-5) anti–factor Xa levels were sampled at 4.4 ± 1.3 hours after a dose, with a mean anti–factor Xa level of 0.52 ± 0.23 U/mL. A 1-compartment model best fit the data, and significant covariates included allometrically scaled weight, serum creatinine, and hematocrit on clearance, and platelets on volume of distribution. Simulations were run for patients both without and with reduced kidney function (creatinine clearance of ≤30 mL/min/1.73 m2). A dose of 1 mg/kg/dose every 12 hours had the highest probability (72.3%) of achieving an anti-Xa level within the target range (0.5-1 U/mL), whereas a dose reduction of ~30% achieved the same result in patients with reduced kidney function. Conclusions: Pediatric patients should initially be dosed at 1-mg/kg/dose subcutaneously every 12 hours for treatment of thromboembolism followed by anti-Xa activity monitoring. Dose reductions of ~30% for creatinine clearance ≤30 mL/min/1.73 m2 are required.