Gentamicin pharmacokinetics: effect of aging in patients with normal renal function

The effects of aging on gentamicin total-body clearance, volume of distribution, and half-life were examined in 173 febrile patients with gram-negative infections. All had normal renal function, normal hematocrit levels, near-ideal body weights, and were not receiving concurrent penicillin therapy. In the 51 patients who were 20-39 years old, the mean clearance of gentamicin was 1.29 ml/min/kg, the volume of distribution was 0.23 l/kg, and the half-life was 2.2 hours. In the 59 patients 40-59 years old, these values were 1.35 ml/min/kg, 0.27 l/kg, and 2.1 hours; in the 63 patients 60-79 years old, they were 1.31 ml/min/kg, 0.26, and 2.4 hours. No significant difference was observed for any of the measures among the three age groups (P less than 0.05, analysis of variance). Linear regression revealed poor correlations between the individual measures and age. Since there is no change in gentamicin pharmacokinetics with aging, dosages do not need to be changed arbitrarily for older patients who have normal renal function.