Topical aminoglycoside ototoxicity: Attempting to protect the cochlea

Cochlear damage following topical application of aminoglycoside antibiotics to the round window membrane is a recognized phenomenon in both animal exp eriments and clinical reports. The authors have recently reported the abili ty of the free radical scavenging agent, alpha lipoic acid, to protect agai nst the cochleo-toxic side effects of systemically administered aminoglycos ide antibiotics. This study attempts to determine if the protective effect of this free radical scavenging agent is also seen following topical aminog lycoside application. Animals were implanted with osmotic pumps which deliv ered 2.5 mu l/h solution of either neomycin 5% or neomycin plus alpha lipoi c acid (50 mg/ml). Control animals received normal saline solution. Drug so lutions were presented directly to the round window membrane over a 7-day p eriod. Auditory sensitivity was monitored using compound action potentials (CAPs) of the auditory nerve recorded through an implanted chronic electrod e terminating at the round window. Sixteen animals were entered into the st udy and randomized to one of the above groups. All animals receiving neomyc in solution, with or without alpha lipoic acid, maintained normal threshold s for the first 3 days of the treatment period. Animals receiving neomycin solution alone experienced profound and rapid deterioration in auditory sen sitivity, which was maximal by day 6. Animals receiving neomycin plus alpha lipoic acid also experienced significant cochlear damage; however, the rat e of deterioration was slower than that seen in the group receiving neomyci n alone. All control animals receiving saline maintained good hearing thres holds throughout the treatment period.