Effect of exchange transfusion on serum gentamicin concentrations.

To determine whether an exchange transfusion increases the rate of elimination of gentamicin, we measured drug (and bilirubin) concentration either before and during, or during and after a standard two-volume exchange procedure in 7 newborns. In an additional 5 infants, serum was obtained only on initiation and conclusion of the procedure. The mean decrement in serum gentamicin concentration with the procedure was 2.2 micrograms/ml; this was 25.7% of the original mean concentration. The mean elimination rate constant during the procedure was 0.342 h-1, a value significantly greater (p = 0.013) than the mean rate before or after the procedure, 0.104 h-1. We conclude that the exchange transfusion procedure significantly increases the rate of gentamicin elimination. The decrement produced by the procedure may result in subtherapeutic concentrations, if the initial values are marginally efficacious.