Pharmacokinetic properties of netilmicin in newborn infants

Netilmicin and gentamicin susceptibilities of 258 gram-negative organisms and 25 strains of Staphylococcus aureus were nearly identical. The pharmacokinetic properties of netilmicin were evaluated in 101 newborn infants and related to birth weight, gestational age, chronological age, and route of administration. Mean peak serum concentrations of 5.6 to 6.9 and 7.8 to 8.4 mug/ml were observed 30 min after 3- and 4-mg/kg doses, respectively, were given intramuscularly. The peak concentrations were directly related to gestational age. The average serum half-life values varied from 3.4 to 4.7 h and in general were inversely related to birth weight, gestational age, and postnatal age. The pharmacokinetics of netilmicin in 10 infants were similar after intramuscular and intravenous administration. A comparative study of netilmicin and gentamicin in seven neonates revealed greater variability in serum concentrations of gentamicin and a shorter half-life for netilmicin. There was evidence of accumulation of netilmicin in 12 low-birth weight, premature infants who received 4-mg/kg doses for an average of 6.4 days. Serum and urine levels of netilmicin were measured up to 11 days after discontinuation of the drug. These data are well characterized by a two-compartment model. Additional studies of efficacy and long-term toxicity of netilmicin in neonates are necessary.