Age-dependence of renal tubular reabsorption of nitrofurantoin.

Nitrofurantoin is rapidly excreted in adult rats. However, in 5 to 15 days old rats the renal excretion of nitrofurantoin is diminshed by a high rate of reabsorption. Because nitrofurantoin has a pKa of 7.2 its tubular reabsorption is influenced by the urine pH but is independent of urine flow. About 50% of an administered dose of nitrofurantoin is recovered as metabolites in the urine of both young and adult rats. Probenecid blocks the active tubular secretion of nitrofurantoin independently of age and reduces its rate of renal clearance. Induction of drug metabolizing enzymes by pretreatment with phenobarbital was without effect either on the metabolism or renal excretion of nitrofurantoin nor could the renal excretion of this drug be diminished by repeated administration. The age-dependent difference in the rate of renal excretion of nitrofurantion is due to the high rate of tubular reabsorption in the young animals. This study provides experimental support for the therapeutic use of nitrofurantoin in the neonatal period.