Methodology for studying the effects of topically applied ear drops on otoacoustic emissions in guinea pigs

Testing of otoacoustic emissions (OAE) has been successfully applied to study outer hair cell function. We used this methodology to evaluate and compare the effect of topically applied normal saline, and gentamicin- and ciprofloxacin-containing drops into the middle ear of guinea pigs. All three solutions similarly decreased the distortion product OAE (DPOAE) and all three caused an inflammatory reaction in the guinea pig's middle ear. OAE failed to detect adequately the ototoxicity of topically administered drops in this animal model because the opening of the bulla affected DPOAE, and both inflamed middle-ear mucosa and osteoneogenesis caused a decrease in DPOAE amplitude. This is the first report examining the influence of topically used otic drops on inner ear function as demonstrated by OAE.