Ototoxic effects from gentamicin ear drops

Reason for posting: Gentamicin ear drops can cause serious side effects (e.g., vertigo, imbalance, ataxia, oscillating vision, hearing loss and tinnitus) when used by patients with perforated tympanic membranes or tympanostomy tubes.1 Despite previous warnings2^,3^,4 ototoxic adverse events continue to occur. The incidence of such events is unknown, but 20 cases have been reported in Canada since 1981,5 with 17 involving vestibular disorders and 3 involving hearing loss. In most cases the conditions being treated were middle-ear disorders with otorrhea; in 1 case gentamicin ear drops were being given to treat Ménière's disease (along with high-dose intratympanic gentamicin infusions). Six patients had used the drops for no more than 5–7 days. The damage was often persistent: in 16 patients the symptoms had not resolved at the time the case was reported to Health Canada.5

The drug: Several preparations of topical gentamicin sulfate solution are marketed in Canada to treat superficial ear and eye infections. Indications for otic preparations include otitis externa6 (“swimmer's ear”). Preparations that include a steroid (e.g., betamethasone) are indicated for acute otitis externa, eczematoid dermatitis, seborrheic dermatitis and contact dermatitis with secondary infection6 and are often prescribed for off-label use to treat chronic suppurative otitis media.7 Prolonged use of these combination topical agents can result in a secondary fungal infection and mycelial plug,7 and use of any gentamicin ear drops can lead to the development of aminoglycoside-resistant organisms.8

Although the risk of ototoxic effects from aminoglycoside otic preparations has long been recognized,9 its importance may have previously been underappreciated. In a survey of 2235 otolaryngologists in the early 1990s, 84% reported using ototopical agents in the presence of a perforated tympanic membrane, and only 3.4% reported having witnessed irreversible ear damage caused by such agents.10

What to do: Acute and uncomplicated otitis externa is often prevented with a few drops of vinegar in each ear after swimming and can be treated with an antiseptic solution such as aluminum acetate.7 When gentamicin ear drops are indicated otoscopic examination is essential, because aminoglycoside ear drops are contraindicated in patients with a perforated tympanic membrane (including those with tympanostomy tubes). The treatment duration should be as short as possible, often less than 7 days, and the drug should be stopped immediately if ototoxic symptoms develop. Patients should be assessed for adverse effects after the first 5–7 days of use, and regularly thereafter if treatment is prolonged. Audiometric assessment is not an appropriate screening tool for ototoxicity,11 because ototoxic effects of topical gentamicin solutions appear to be primarily vestibular rather than cochlear.3^,4 Although ototoxicity in patients with intact tympanic membranes has not yet been reported, patients taking the drug for chronic otitis media often systemically absorb detectable levels of the drug.11 Thus, it may be appropriate to warn all patients taking gentamicin ear drops of possible ototoxic effects. When a topical agent is required in patients with a perforated tympanic membrane, non-ototoxic ear drops such as ciprofloxacin solution may preferable.

Eric Wooltorton CMAJ Editorial Fellow