Evaluation of gentamicin-induced nephrotoxicosis in toadfish

To evaluate the nephrotoxic effects of various dosages and regimens of gentamicin in kidneys of toadfish (Opsanus tau).

Prospective, randomized, controlled trial.

45 clinically normal toadfish.

Gentamicin was administered at dosages of 2.5, 5, 15, and 50 mg/kg of body weight, i.p., and 3.5 mg/kg, i.m. Fish were euthanatized at various periods (2, 3, 7, 14, and 28 days) after gentamicin administration. Four hours prior to euthanasia, each fish received 100 mg of bromodeoxyuridine/kg, i.p. Histologic evaluation for signs of toxicosis was performed on samples of renal tissue.

Extensive necrosis was evident in the proximal tubes in each fish injected with gentamicin at every time period, regardless of route of administration. By 28 days after injection of gentamicin, sections of kidney that were examined were essentially devoid of proximal tubules. Bromodeoxyuridine staining was detected in collecting duct epithelial cells, but repair along nephrons was not observed.

Toadfish kidneys are extremely susceptible to gentamicin-induced nephrotoxicosis. Fish in this study did not have overt clinical signs of nephrotoxicosis, but sustained massive tubular necrosis when given the exact therapeutic dose that has been used for channel catfish. There are substantial risks of inducing iatrogenic renal injury in fish species for which therapeutic dosages of gentamicin have not been determined.