This study characterizes the pharmacokinetics of bumetanide after an intravenous dose of 0.05 or 0.10 mg/kgto 14neonates (weight range 820-4,000 g; gestational age 26-40 weeks) during the first week of life. Blood samples and urine were collected for up to 12 h after dosing. Estimated serum clearance was 0.2–1.0 ml/min·kg (range), volume of distribution was 0.22 1/kg (range 0.11–0.32 1/kg), and the harmonic mean half-life was 6–7 h (range of 4–19 h). Nonrenal clearance accounted for 58–97% of the serum clearance with the presence of certain oxidative metabolites of bumetanide in the urine. These findings suggest higher dosing requirements and prolonged intervals as compared to adults. Utilizing these pharmacokinetic data, pharmacodynamic and ototoxicity studies should be conducted to establish a safe and effective neonatal dose.

These data suggest that the proposed postconceptional age protocol is reproducible and reliable in achieving therapeutic gentamicin serum concentrations in neonates.