Pharmacokinetic assessment of netilmicin in newborns and older children

The pharmacokinetics of netilmicin were analyzed in 30 children, including 13 premature and seven gestationally mature newborns. Ten were children ranging in age from 3.5 months to 13 years. The newborns exhibited more variation in serum levels than the older children, and the premature babies more than those born at term. The serum half-life (t1/2), tended to show higher values in premature than in mature newborns, although this was not statistically significant. The newborns had a t1/2 of 5.9 hours, compared to 2.5 hours in the older children. There was no statistically significant difference in distribution volumes or coefficients between the two groups of newborns who had an insignificantly higher relative apparent beta-phase distribution volume coefficient of 0.420 l/kg, compared to 0.377 l/kg in the older children. All had distribution coefficient values within the same range. The total body clearance in absolute terms, and when referred to body surface of 1.73 m2, was significantly lower in the newborns than in the older children, but the clearance, when referred to body weight, was of the same order in the babies and older children. The age differences affect dosage. Dosage schedules based on pharmacokinetics are proposed for gestationally premature babies, mature newborns, and older children. Premature infants can receive 2.5 mg/kg body weight and gestationally mature newborns 3.0 mgkg, both every 12 hours; the monitoring of serum concentrations is mandatory. Children aged three months and older can receive 3.0 mg/kg every eight hours.