The renal handling of tobramycin (TOB), an aminoglycoside antibiotic (AG), was studied using a single‐pass isolated perfused rat kidney with moment analysis. In the bolus administration study at tracer concentration (7.4 μM), 32% of the glomerular‐filtrated TOB remained in the lumen, but no TOB was found in the vein. This ratio of the luminal uptake was reduced in a dose‐dependent manner. Other aminoglycosides such as gentamicin inhibited this uptake, but tetraethylammonium and glucosamine had no effect. In addition, under the alkalinuria condition, TOB uptake was decreased to 67% of the control value. This indicated that TOB has mainly been taken into the renal epithelial cells from their luminal site and that this uptake process was saturable and specific for AGs which have more than one cationic group. The present findings should be helpful in developing a method to reduce the nephrotoxicity of AGs and to identify their toxicity mechanisms.
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