It had been suggested that disinfectants which could trickle into the middle ear through a perforated drum during the skin sterilization preceding otosurgery might cause inner ear damage resulting in deafness. In animal experiments it has been shown that chlorhexidine, benzethonium- and benzalkonium chloride, when introduced into the tympanic cavity of guinea pigs, will cause rather extensive damage to the neuroepithelial receptors of the inner ear. In the present study, iodine, frequently used for skin disinfection, has been investigated as regards ototoxicity by locally exposing the middle ear in guinea pigs. The duration of exposure was 10, 30, or 60 min. The animals were sacrificed 2 weeks later and the organs of Corti and neuroepithelial receptors of the vestibular part of the inner ear were studied as surface preparations in phase-contrast microscopy. It was found that slight damage had occurred in the basal parts of the organ of Corti of those ears exposed to iodine or iodophor in 70% alcohol for 60 or 30 min and damage to the vestibular receptors was observed in ears exposed to iodophor in 70% alcohol for 60 min. In ears exposed to iodine or iodophor in aqua dest., no damage to the inner ear sensory epithelia was revealed.

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In earlier investigations by the author it has been shown that chlorhexidine, when introduced into the middle ear of guinea pigs, caused serious damage to the inner ear. The present investigation was performed in order to study if the quaternary ammonium compounds benzethonium chloride and benzalkonium chloride, frequently used for skin disinfection, can also induce inner ear damage when introduced into the tympanic cavity of guinea pigs. The disinfectants in question, at a concentration of 0.1 % and in a solution of aqua dest. or 70% alcohol, were introduced into the animals' middle ear for exposure times of 10, 30, or 60 min. The animals were sacrificed 2 or 9 weeks after the exposure and the organ of Corti and vestibular neuroepithelia were studied as surface preparations with phase contrast microscopy. It was found that most of the ears exposed to the disinfectants had suffered damage, affecting both the vestibular and cochlear parts of the inner ear. The extent of the damage was related both to the duration of exposure and to the length of the animals' survival after the exposure. Furthermore it was found that the tympanic cavity and the perilymphatic spaces of vestibulum and cochlea were pathologically changed.

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Loss of hearing in a 43 year old man during treatment with metoprolol was dose related and disappeared within a few months after the drug had been stopped. The hearing impairment was of mixed type, with an air bone gap without any disorder of the middle ear observable by conventional clinical methods. Similar scattered reports from international sources on loss of hearing during treatment with P blockers are also presented.