Uptake of gentamicin in foetal and newborn rats after a single intraperitoneal injection

The aim of the present investigation has been to examine 1) the placental passage and uptake of gentamicin in foetal rat tissues and 2) uptake and organ distribution of this drug in neonatal rats with special reference to the kidney. After a single intraperitoneal injection of tritium-labelled gentamicin to the mother, we found a rapid passage of radioactivity across the rat placenta, but no pronounced tendency to accumulation in the foetus. After administration of 10 micrograms or 100 mg gentamicin per kg body weight to pregnant rats at day 11 or 13, respectively, of gestation, the maximal concentrations of the drug recovered in individual foetuses were 0.05 and 300 ng per mg wet weight. Ten and 90 min. after administration the uptake of gentamicin in the kidney cortex of the mother was 25 and 118 fold higher, respectively, than the corresponding uptake in the foetal kidney after 19 days of gestation. After a single intraperitoneal injection, gentamicin uptake in the kidney cortex of neonatal rats resembled that seen in adult animals, with a rapid initial phase followed by a relatively stable plateau, although the maximal uptake was only about 10% as large in the neonates.