Perhaps not unless their is impaired renal function or any condition that causes impairment of maintenance of water balance.

Dear Sara,

Really, the dilution could lead to the change in toxicity due to saline loading (it seems that the volume in your studies reached 0,15 ml/10 g), despite the moderate volume it can enhance the excretory renal function, and it is well known that increased tubular flow counteracts nephrotoxic stimuli.

Some time ago we worked with such model and the dose of 80 mg/kg was able to induce nephrotoxicity after 7 days (including hypercreatininemia, GRR and water reabsorption, relative kidney weight  etc.), still we used intramuscular way of administration and random-bred mice (so I can not say anything about the differences between strains) and took samples several hours after the last injection. As much higher dose was used in your studies it can be supposed that some parameters of kidney function for all that were disturbed (especially tubular sodium transport).

Besides, in that work we have compared gentamicin produced by four different pharmaceutical factories and they showed significant differences in toxicity (as well as in activity), so this also can contribute (although such differences should not be present on pharmaceutical markets and I hope that generally situation is better).

Regards,

Olga Tovchiga

This might be the reason for your variance in nephrotoxicity.

J Am Soc Nephrol. 2006 Oct;17(10):2697-705. Epub 2006 Sep 13.

A non-nephrotoxic gentamicin congener that retains antimicrobial efficacy.

Sandoval RM1, Reilly JP, Running W, Campos SB, Santos JR, Phillips CL, Molitoris BA.

Thank you all for your very helpful answers. 

Dear Olga, 

What were the mice strain you have used in your experiments?

Thank you in advance

Dear Sara,

Unfortunately, we had only an outbred stock of mice.

Later for in-depth research I used rats and the results were more stable (together with higher samples volume and easier collection of 24-hours urine samples)