Accuracy of pharmacokinetic dose determination of gentamicin in geriatric patients

Gentamicin pharmacokinetics and the predictive performance of the Sawchuk-Zaske dosing method for gentamicin were compared in elderly and young patients with stable normal serum creatinine concentrations. The predicted peak gentamicin concentrations in both young and elderly patients were not significantly different from the actual measured concentrations. The predicted trough concentrations for both the young and elderly were significantly different from the measured trough concentrations. However, the magnitude of this difference (0.2 micrograms/mL) is not considered to be clinically significant. A trend toward greater underprediction of trough gentamicin concentrations in elderly patients was evident. The mean increase of 15 percent in the gentamicin half-life at steady-state compared with the initial pharmacokinetics analysis in elderly patients was significantly larger than the increase in half-life in the young patients. The Sawchuk-Zaske method was equally accurate in determining the gentamicin dosing regimen in young elderly patients with normal serum creatinine concentrations.