Effect of age and renal function on gentamicin pharmacokinetic parameters

The effect of age and renal function on gentamicin pharmacokinetic parameters were studied in 125 patients with various degrees of renal function. Patients were grouped according to age. Group 1 ranged from 18-40 years (46 patients), group 2 ranged from 41-64 years (53 patients) and group 3 ranged from 65-92 years (26 patients). Elimination rate constant (K) were 0.28 +/- 0.01 h-1 (mean +/- SEM), 0.23 +/- 0.02 h-1, and 0.16 +/- 0.01 h-1 for groups 1, 2 and 3, respectively. Total body clearance (Clt) were 86.21 +/- 5.0 ml/min, 62.41 +/- 4.36 ml/min, and 46.08 +/- 3.89 ml/min, for group 1, 2 and 3, respectively. No significant differences were found between groups with respect to apparent volume of distribution. There was a significant decrease in creatinine clearance (Clcr) with increase in age. Linear regression analysis revealed good correlations between age of the patients and K (r = 0.4132, p less than 0.05), between age and Clt (r = 0.3999, p less than 0.05) and between age and Clcr (r = 0.5241, p less than 0.05). However, poor correlations between age and apparent volume of distribution and between age and serum creatinine concentration were obtained. Significant relationships were also obtained between the composite parameters Clt/age and K/age vs Clcr (r = 0.7064, p less than 0.001, and r = 0.7200, p less than 0.001, respectively). On the other hand, no significant relations were found between K/Clcr and Clt/Clcr vs age of the patients. These findings suggest that the elimination of gentamicin is independent of age of the patient but is highly dependent on renal function.