Gentamicin Pharmacokinetics in Elderly Patients with Normal Renal Function

Abstract

Objective:

To establish the pharmacokinetic parameters of gentamicin in elderly patients and to compare predicted concentrations based on the Dettli method, with actual concentrations.

Design:

Measurement of gentamicin concentrations and pharmacokinetic parameters in a consecutive patient sample with comparison to ones predicted by the Dettli method.

Setting:

Medical and surgical units in a Veterans Affairs Medical Center.

Patients:

Forty-six consecutive elderly men treated with gentamicin for documented or presumed infection and had stable, normal renal function.

Main Outcome Measures:

The following information was calculated or measured: elimination rate constant (k_el), elimination half-life, volume of distribution (V_d), and peak and trough concentrations.

Results:

The mean k_el (0.16 ± 0.05 h⁻¹) was not significantly different (p=0.2) from the Dettli method prediction, and the mean V_d (0.36 ± 0.1 L/kg) was 37 percent higher than that usually reported. Actual peak and trough concentrations were significantly lower (both p<0.01) than predicted concentrations.

Conclusions:

Based on our findings, higher than recommended loading doses and longer dosage intervals may be required in the elderly. The Dettli method is useful to estimate k_el in the elderly.