Monitoring serum levels of gentamicin to develop a new regimen for gentamicin dosage in newborns.

The newborns studied had gestational ages ranging between 23-44 weeks, weights ranging between 725-4510 g, and were treated with standard doses of gentamicin (5.2 +/- 1.0 mg/kg/day). The gentamicin serum peak and trough levels were unrelated to administered doses, and a large proportion of patients had low (peak less than 4 micrograms/ml in 12%) or potentially toxic concentrations (trough greater than 2 micrograms/ml in 55%). The pharmacokinetic parameters (t1/2e, 8.2 +/- 4.8 h and Vd, 0.64 +/- 0.22 L/kg) varied markedly between patients. The newborn's weight, age, gestational age, and serum creatinine were factors of importance for the variability of gentamicin serum levels. The newborns were divided into four groups: gestational period less or more than 37 weeks and age below or above 7 days. These groups had different gentamicin serum levels and pharmacokinetic parameters. The results suggest that a gentamicin dosage regimen based on the division of newborn patients into subgroups or calculated from individual pharmacokinetic characteristics would decrease the risk of obtaining potentially toxic or subtherapeutic gentamicin concentrations after the use of standard doses.