Gentamicin and tobramycin nephrotoxicity. A morphologic and functional comparison in the rat.

Fischer 344 rats were treated with tobramycin or gentamicin, 40 mg/kg/day, for up to 10 days or with tobramycin, 120 mg/kg/day, for up to 14 days. Serum creatinine and BUN at the time of sacrifice were determined, and kidney tissues were examined by light and electron microscopy. Rats receiving gentamicin demonstrated progressive renal proximal tubular necrosis which was nearly universal at the end of 10 days. Their BUN and creatinine levels rose progressively over the same period. Even at the higher dosage, tobramycin therapy resulted in only rare foci of proximal tubular necrosis and minimal elevation of BUN and creatinine. Although they occurred later and were substantially less severe, the ultrastructural changes induced by tobramycin were the same as those seen following gentamicin administration. These results indicate that the mechanism of tobramycin-induced renal injury is probably similar to that of gentamicin and that tobramycin is significantly less nephrotoxic in this experimental model.