EVALUATION OF GENTAMICIN-INDUCED NEPHROTOXICOSIS IN TOADFISH

Objective-To evaluate the nephrotoxic effects of various dosages and r egimens of gentamicin in kidneys of toadfish (Opsanus tau). Design-Pro spective, randomized, controlled trial. Animals-45 clinically normal t oadfish. Procedure-Gentamicin was administered at dosages of 2.5, 5, 1 5, and 50 mg/kg of body weight, IP, and 3.5 mg/kg, IM. Fish were eutha natized at various periods (2, 3, 7, 14, and 28 days) after gentamicin administration. Four hours prior to euthanasia, each fish received 10 0 mg of bromodeoxyuridine/kg, IP. Histologic evaluation for signs of t oxicosis was performed on samples of renal tissue. Results-Extensive n ecrosis was evident in the proximal tubules in each fish injected with gentamicin at every time period, regardless of route of administratio n. By 28 days after injection of gentamicin, sections of kidney that w ere examined were essentially devoid of proximal tubules. Bromodeoxyur idine staining was detected in collecting duct epithelial cells, but r epair along nephrons was not observed. Clinical Implications-Toadfish kidneys are extremely susceptible to gentamicin-induced nephrotoxicosi s, Fish in this study did not have overt clinical signs of nephrotoxic osis, but sustained massive tubular necrosis when given the exact ther apeutic dose that has been used for channel catfish. There are substan tial risks of inducing iatrogenic renal injury in fish species for whi ch therapeutic dosages of gentamicin have not been determined.