Use of enoxaparin in a preterm infant

To describe the use of enoxaparin to treat suspected thrombosis in a preterm neonate.

A 29-week-gestation white infant with a family history of protein S deficiency lost color and blood flow to the right hand several hours after removal of the umbilical artery catheter. Although normal color returned to all except the distal first, second, and third fingers after warming, Doppler flow showed a radial artery defect, indicating a lack of blood flow. Enoxaparin 1 mg/kg intravenously every eight hours was then started. Heparin concentrations measured via anti-Xa assay drawn four and eight hours after a dose were 0.78 and 0.39 units/mL, respectively. Pharmacokinetic parameters calculated from these concentrations using a one-compartment model were elimination half-life four hours, volume of distribution 0.13 L/kg, and clearance 0.022 L/kg/h. No adverse effects were noted. Blood flow eventually returned, leaving only the third fingertip chronically injured.

Differences between the neonatal and adult hemostatic systems contribute to an increased risk of thromboembolic events and an altered sensitivity to heparin anticoagulation in the neonate. Although heparin is currently the anticoagulant of choice, it may produce several adverse effects, such as hemorrhage and thrombocytopenia, which may be avoided by use of low-molecular-weight heparins (LMWHs). However, despite the efficacy and improved safety profile of LMWHs in adults, data regarding their use in children and neonates are scarce. This case demonstrates that enoxaparin can be used safely and effectively in a preterm infant through appropriate monitoring of heparin concentrations to adjust dosages. A larger volume of distribution of enoxaparin was noted in this neonate than in adults.

Enoxaparin 1 mg/kg intravenously every eight hours was used safely in this preterm infant with suspected thrombosis, suggesting that more than one dosing regimen may be appropriate in this population.