Comparative effects of tobramycin and gentamicin on glomerular ultrastructure.

To examine and compare the effects of tobramycin and gentamicin and glomerular endothelium, these drugs were given to rats at dosages of 80, 40 or 4 mg/kg per day for 10 days, when detailed, quantitative scanning electron microscopic studies of glomerular architecture were performed. Gentamicin caused significant dose-related decreases in endogenous creatinine clearance, but tobramycin did not. Gentamicin administration resulted in a decrease in the diameter and density of endothelial fenestrae at all dosages tested. The changes were dose-dependent and accounted for a decrease in filtration area ranging from 75% at 4 mg/kg per day to 36% at 80 mg/kg per day. Tobramycin administration caused only minor alterations, even at the high dosages, which did not significantly reduce filtration area. Thus, the difference in effect of glomerular filtration rate caused by gentamicin and tobramycin corresponds closely to differences in their effects on glomerular ultrastructure.