Ototoxicity of Topical Gentamicin in the Cat

Abstract

In an attempt to find the nontoxic topical dose of gentamicin for the cat, we studied the histological effects of topical gentamicin on the vestibular function and temporal bone and compared them to the effects of neomycin and water. The drug was applied in the bulla, which contains the round window, and thus simulates application to the middle ear in the human. Pilot studies showed that an aqueous solution of gentamicin appeared toxic at concentrations between 3% and 10%. In the definitive series, 0.4 ml of gentamicin was applied daily as a 6% solution for 19 days or less and as a 3% solution for 30 days. This series showed topical gentamicin to be most toxic to the cochlea and saccule. Its ototoxic effects at these doses were local and approximately twice as severe as those of 0.4 ml of 3% neomycin applied topically for 30 days, where a systemic as well as a topical effect was found.