Dosing implications of altered gentamicin disposition in patients with cystic fibrosis.

A pharmacokinetic approach was used for gentamicin dosing in 19 children and young adults with cystic fibrosis. A one-compartment open-model analysis of steady-state gentamicin pharmacokinetics revealed a significantly larger apparent volume of distribution and total plasma clearance for patients with CF as compared to a similar population of children without the disease. The increase in the apparent volume of distribution for patients with CF produced a larger daily gentamicin dose requirement to maintain similar steady-state levels as compared to children without the disease. Significant differences in the elimination rate constant and half-life for gentamicin were not found between these populations. Linear correlations between creatinine clearance and kel for gentamicin, and total body body weight and the apparent volume of distribution were demonstrated for children with varying degrees of stable renal function but not patients with CF. Altered gentamicin disposition peculiar to CF precludes application of currently used dosing nomograms or guidelines derived from normal populations, and emphasizes the need for individualized gentamicin therapy guided by a pharmacokinetic approach in these patients.