The frequency of aminoglycoside-associated hearing loss is 2-45%. Since gentamicin-induced ototoxicity in most cases only involves vestibular function, the symptoms are easily overlooked in severely ill patients who are unable to sit. If diagnosed early, the vestibular damage is usually reversible. In some cases, severe long-term disability has been described (6). Six patients presented with unilateral vestibulotoxicity after systemic gentamicin therapy (7). All had ataxia and oscillopsia, but none had a history of vertigo. The authors suggested that a subacute course of vestibulotoxicity with time for compensation or asymmetrical recovery of vestibular function after bilateral vestibular loss could have explained the lack of vertigo in these patients.
The risk of ototoxicity from gentamicin in children is probably less than in adults. In many studies of serious neonatal infections treated with gentamicin there have been very few cases that have provided unequivocal evidence of gentamicin-induced ototoxicity. Gentamicin can be an excellent drug in neonatal sepsis, and its potential toxicity should not preclude its use when it is needed.
Gentamicin ear-drops can cause serious adverse effects (for example vertigo, imbalance, ataxia, oscillating vision, hearing loss, and tinnitus) when they are used by patients with perforated tympanic membranes or tympanostomy tubes (8).
The symptom complex known as visual vestibular mismatch can be caused by peripheral vestibular disease. In a retrospective study of 28 patients with Meniere's disease, 17 had visual vestibular mismatch; gentamicin therapy increased the number of positive answers (9).
In a retrospective analysis of 85 patients treated with intratympanic gentamicin, using a fixed-dose regimen of 26.7 mg/ml tds on 4 consecutive days, hearing loss occurred in 26% of individuals (10).
The characteristics of ototoxicity of topical gentamicin have been studied retrospectively in 16 patients (11). All used ear-drops for more than 7 days before the development of symptoms, and all had some degree of vestibulo-toxicity, but only one had a worsening of cochlear reserve. Even if the tympanic membrane is intact, one should hesitate to use gentamicin in ear-drops or in other topical forms for the treatment of otitis media.
In patients with acute bacterial conjunctivitis there were adverse drug reactions in 4 of 103 treated with gentamicin (12). The adverse effects included redness, itching, and burning, and none was serious.
In two animal studies methylcobalamin or dimethyl-sulfoxide inhibited the ototoxic adverse effects of genta-micin (13,14).
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