Several biological responses to drugs are dependent on the age of the individual. Renal excretion of amikacin occurs mainly through glomerular filtration and this function is diminished in the young animal. We evaluated the renal response to amikacin in the unanesthetized infant rat (21-day-old) and we compared it with that of the adult rat. Either amikacin (7.5 and 75.0 mg/kg body weight, i.m.) or vehicle were administered to infant rats and the effects on sodium, potassium and water balance were assessed. Creatinine clearance (Ccr) was calculated. Amikacin induced an increment in sodium absolute excretion, whereas the Ccr decreased. In the infant rat the effects were more marked. Chang es in FENa were more marked than those in Ccr, suggesting a direct effect of amikacin on the tubular reabsorption of electrolytes in addition to deleterious effects on glomerular dynamics. Our results suggest that amikacin induces more changes in renal function in the infant than in the adult rat and therefore it might be convenient to carefully evaluate the renal condition in the patients that receive this drug.
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