Pharmacokinetics of once-a-day netilmicin (6 mg/kg) in neonates

The pharmacokinetics of once a day netilmicin (6 mg/kg) was studied in 21 neonates. The babies were divided into three groups according to gestational age: group I aged > 36 weeks; group II between 34-36 weeks and group III < 34 weeks. Serum concentrations were variable between patients and the concentration 24 h after the first dose ranged from 0.8 to 3.8 mg/L with only two babies having concentrations of < 1 mg/L while seven had concentrations of > 2 mg/L. There were also large patient-to-patient variations in serum half-life, volume of distribution, area under the curve and relative plasma clearance such that these parameters could not be correlated to gestational age or weight. Absolute plasma clearance was correlated with both gestational age and weight. There was evidence of accumulation between the first and second dose for all three patient groups and for patients of gestational age < 34 weeks (group III) these observations were statistically significant. A netilmicin dosage of 4.5 mg/kg once a day may be more suitable for all neonates supported by assay of serum concentrations.