The penetration of gentamicin and neomycin into perilymph across the round window membrane.

Many commonly employed otic drops contain aminoglycoside antibiotics that may be toxic to the inner ear. A variety of chemicals such as ionic solutions, certain anesthetics, and epinephrine have been shown to diffuse across the round window membrane into the perilymph. Twelve adult cats were studied in this experiment. The auditory bulla was exposed and solutions containing gentamicin or neomycin concentrations similar to that commonly used in otic drops were applied to the round window niche for 15 minutes and washed with saline solution. The gentamicin and neomycin concentrations in the round window niche wash and the perilymph were then assayed by a radioenzymatic method. Concentrations of both antibiotics were observed in the perilymph. Thus, the round window membrane is a route through which these ototoxins may gain access to the inner ear.