Gentamicin interval in newborn infants as determined by renal function and postconceptional age

We evaluated the relationship between gentamicin pharmacokinetics and glomerular filtration rate in newborn infants to estimate the appropriate interval of administration in neonates with renal insufficiency. Gentamicin half-life (Gt 1/2) could be predicted from plasma creatinine concentration (Pcr) (r=0.78); the prediction was minimally but significantly increased (r=0.81) by adding postconceptional age to a multiple regression analysis. Infants with a postconceptional age of 29 weeks or more and a Pcr of 1 mg/dl or more had significantly greater trough and peak gentamicin levels than those with a Pcr less than 1 mg/dl. If gentamicin is indicated in a patient with renal insufficiency, the interval of administration should be 2-3 G_t 1/2, which can be estimated from Pcr (G t 1/2=2.0+7.7 Pcr). The interval can then be adjusted according to peak and trough gentamicin levels.