Use of enoxaparin in a preterm infant

OBJECTIVE: To describe the use of enoxaparin to treat suspected thrombosis in a preterm neonate. CASE DESCRIPTION: A 29-week-gestation white infant with a family history of protein S deficiency lost color and blood flow to the right hand several h ours after removal of the umbilical artery catheter. Although normal color returned to all except the distal first, second, and third fingers after wa rming, Doppler flow showed a radial artery defect, indicating a lack of blo od flow. Enoxaparin 1 mg/kg intravenously every eight hours was then starte d. Heparin concentrations measured via anti-Xa assay drawn four and eight h ours after a dose were 0.78 and 0.39 units/mL, respectively. Pharmacokineti c parameters calculated from these concentrations using a one-compartment m odel were elimination half-life four hours, volume of distribution 0.13 L/k g, and clearance 0.022 L/kg/h. No adverse effects were noted. Blood flow ev entually returned, leaving only the third fingertip chronically injured. DISCUSSION: Differences between the neonatal and adult hemostatic systems c ontribute to an increased risk of thromboembolic events and an altered sens itivity to heparin anticoagulation in the neonate. Although heparin is curr ently 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 impro ved safety profile of LMWHs in adults, data regarding their use in children and neonates are scarce. This case demonstrates that enoxaparin can be use d safely and effectively in a preterm infant through appropriate monitoring of heparin concentrations to adjust dosages. A larger volume of distributi on of enoxaprin was noted in this neonate than in adults. CONCLUSIONS: Enoxaparin 1 mg/kg intravenously every eight hours was used sa fely in this preterm infant with suspected thrombosis, suggesting that more than one dosing regimen may be appropriate in this population.