OTOTOXICITY ASSESSMENT OF A GENTAMICIN SULFATE OTIC PREPARATION IN DOGS

Vestibulotoxic and ototoxic effects often are seen after long-term, hi gh-dose systemic treatment with gentamicin, but toxic effects after to pical use have not been reported in animals, to the authors' knowledge . Vestibular and auditory effects of twice daily otic gentamicin treat ment for 21 days were evaluated in 10 dogs with intact tympanic membra nes and in the same 10 dogs after experimental bilateral myringotomy. Each dog served as its own control; 7 drops of gentamicin sulfate (3 m g/ml in a buffered aqueous vehicle) were placed in 1 ear, and 7 drops of vehicle were placed in the opposite ear. Treatment and control ears were reversed after myringotomy. Vestibular function was evaluated da ily by neurologic examination and behavioral assessment. Auditory func tion was evaluated twice weekly by determination of brain stem auditor y evoked potentials. Gentamicin sulfate placed in the ear of clinicall y normal dogs with intact or ruptured tympanic membranes, in the quant ities used in this study, did not induce detectable alteration of coch lear or vestibular function. Serum gentamicin concentration after 21 d ays of treatment was detectable in only 2 dogs and was an order of mag nitude below documented toxic concentrations.