Persistence of sisomicin and gentamicin in renal cortex and medulla compared with other organs and serum of rats.

Aminoglycoside antibiotics seem to accumulate and persist in the kidney. For a better understanding of this problem, groups of six rats received a single 4 mg/kg i.p. injection of sisomicin and were sacrificed repeatedly from 30 min to 28 days later. Sisomicin concentrations (bioassay) decreased rapidly in the serum, lung and other tissues. There was only a trace at six hours. The situation was totally different for the kidney. Concentrations in the cortex increased up to six hours with a maximum of 99 mug/g, 11 times higher than the peak value in the serum then decreased very slowly to 56, 18, and 7 mug/g, 2, 14 and 28 days, respecitvely, after injection. The concentrations in the medulla were lower than in the cortex but also showed an accumulation and persistence. Similar results were observed with gentamicin. In another experiment, daily injections of sisomicin or gentamicin during seven days demonstrated that the concentrations of both antibiotics six hours after the last injection were nearly three times higher in the cortex and twice as high in the medulla than after a single injection. These data explain why the nephrotoxicity of sisomicin or gentamicin involves chiefly the cortex, increases with the length of the treatment and can persist for several weeks after the last injection. Therapeutic implications need further studies.