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Abstract
Ear drops containing neomycin only rarely cause ototoxicity. The authors report on three patients with a tympanic membrane perforation who developed severe ototoxicity after use of eardrops containing 0.35 per cent neomycin. Mitochondrial DNA analysis revealed that there was no A1555G point mutation in these patients. This finding indicates that application of low concentration neomycin to the middle ear can cause severe inner ear damage even in humans who are not hyper-susceptible to aminoglycosides.
Key words: Neomycin; Cochlea; Hearing Loss, Sensorineural; Vertigo; Mutation; Drug Hypersensitivity
Introduction
Neomycin is one of the most ototoxic drugs in modern medicine. Neomycin ototoxicity has been reported in all the routes of administration: oral, rectal, parenteral, intrapleural, wound irrigation, and aerosol spray. Neomycin primarily causes cochlear damage, especially when renal and gastrointestinal functions are altered.1 Hearing impairment may develop, or continue to progress after systemic or topical application is discontinued.1,2 Kavanagh and McCabe1 reviewed cases of neomycin ototoxicity and concluded as follows: 'the usual latency is from two to six weeks after the onset of neomycin therapy. Since many patients received short courses of the drug, the hearing loss was often noticed days to weeks after the drug was discontinued. The onset of deafness may be severe and sudden but is usually progressive and may progress from six to 10 months, leaving the patient with a profound hearing loss.'
Several commonly used eardrops, including Cortisporin®, contain neomycin. When applied to the middle-ear space of guinea pigs, neomycin readily entered the perilymph in the cochlea through the round membrane3 and at a concentration of 5 mg/ml or more caused dose-dependent ototoxicity.4,5 Despite these experimental findings, hearing loss, vertigo, or both have rarely been reported after use of a neomycin otic suspension. Several large reference works failed to find such cases in humans (reviewed by Lind and Kristiansen6). An inquiry made by Swiss otolaryngologists showed that inner ear damage caused by antibiotic eardrops with ototoxic properties is estimated to occur in only one of 1 000 to 3 000 treatments.7 Merifield et al8 found no increase in the bone conduction thresholds in 44 children with chronic suppurative otitis media treated with five different topical aminoglycosides, four of which contained neomycin at a concentration of 0.33 or 0.35 per cent. Lind...