Nephrotoxicosis associated with topical administration of gentamicin in a cat

A 4-year-old cat was referred for treatment of a large, open wound. The wound had been lavaged twice, approximately 12 hours apart, with approximately 10 ml of 5% gentamicin solution prior to referral, because of infection caused by Pseudomonas spp. Results of initial serum biochemical analyses were within reference ranges, and the cat was anesthetized for surgical wound debridement and closure. Two days later, the cat was azotemic (SUN concentration, 113 mg/dl; serum creatinine, concentration, 9.8 mg/dl) and had a urine specific gravity of 1.008. Granular casts were seen in the urine. The azotemia became more severe over the next 2 1/4 hours, despite treatment for acute renal failure, and the cat was euthanatized. Severe acute proximal tubular necrosis, consistent with gentamicin-induced nephrotoxicosis, was diagnosed histologically. Retrospectively, serum samples obtained for biochemical analyses were assayed for gentamicin concentration. Serum concentration of gentamicin 8 hours after topical lavage was 58.07 micrograms/ml. This was approximately 6 times greater than the desired peak concentration for gentamicin and suggested that gentamicin had been absorbed systemically following topical application.