Gentamicin can cause tinnitus: its label lists ringing and roaring among the signs of inner-ear damage, which is usually permanent. It can also destroy balance function, sometimes sparing hearing, and that is why doctors inject it into the ear on purpose to stop Ménière's vertigo.
These are two different situations. In the first, gentamicin is an antibiotic given into a vein or muscle for a serious infection, and harm to the ear is a side effect. In the second, a small amount is placed in the middle ear of someone with disabling Ménière's disease, and reducing the balance function of that ear is the point. For the wider list of drugs that can cause ringing, see ototoxic medications.
What gentamicin does to the inner ear
Gentamicin belongs to the aminoglycosides, a family of antibiotics that also includes tobramycin, amikacin and streptomycin. The US prescribing information for gentamicin injection says ototoxicity, "both vestibular and auditory", can occur, mainly in people with existing kidney damage and in people with normal kidneys given higher doses or longer courses than recommended. It calls aminoglycoside ototoxicity usually irreversible.
The label lists the warning signs as dizziness, vertigo, tinnitus, roaring in the ears and hearing loss, and says any of them requires the dose to be adjusted or the drug stopped. Hearing loss, it notes, usually starts with the high tones. It also warns that on rare occasions the changes do not show until soon after the course has finished.
Balance can take the larger hit. A case series from a balance disorders clinic, published in 2012, reviewed 103 people seen between 1988 and 2010 with severe loss of balance function in both ears after gentamicin in hospital. All of them had imbalance, oscillopsia (the view seeming to bounce or jump when the head moves, as when walking) or both. None had vertigo. Only three had noticed any change in hearing, and everyone's hearing test was in line with their age. The authors concluded that the drug's ototoxicity was vestibular, not cochlear, and permanent. Because everyone in the series came to a balance clinic, it cannot say how often gentamicin spares hearing in general, only that it can.
A 2019 review of aminoglycoside balance damage makes the same practical point: the symptoms to recognise are unsteadiness and oscillopsia, not hearing loss or spinning. A 2017 systematic review of 27 studies found balance side effects in anywhere from 0 to 60% of people given aminoglycosides, depending on the study. This kind of damage is easy to miss. In the 2012 series, 21 people noticed imbalance during treatment, and in 20 of them the prescribers ignored or dismissed it. Time to diagnosis ranged from 4 days to 15 years.
How often it causes tinnitus
Good figures for gentamicin alone are scarce. A prospective study tested 488 US veterans before, during and after treatment with cisplatin, carboplatin, ototoxic antibiotics (mainly aminoglycosides) or drugs not known to harm the ear. Against the comparison drugs, ototoxic antibiotics carried a borderline 2.81-fold risk of new tinnitus, well below cisplatin's 5.53-fold risk. Chemotherapy and tinnitus covers the platinum drugs.
A single dose is a different picture from a long course. A 2018 systematic review of 36 studies, covering 24,107 adults given one dose of gentamicin (from 1 mg/kg up to 480 mg), found no reported cases of ototoxicity. The 2012 case series is a reminder that "no reported cases" is not "no risk": six of its 103 patients had received only a single dose, and 26 had five doses or fewer. Its authors concluded that gentamicin can harm balance at any dose, in any regimen and at any blood level.
Who is at higher risk
The US label names these risk factors for ear and kidney toxicity:
- existing kidney impairment, especially where dialysis is needed
- higher doses or longer courses than recommended
- advanced age and dehydration
- previous exposure to other ear-toxic drugs
- potent diuretics such as furosemide or ethacrynic acid given at the same time
- other drugs that can harm the ear or kidneys given together or in sequence, including cisplatin, vancomycin and other aminoglycosides
Inherited susceptibility is the other big factor. Certain variants in MT-RNR1, a gene carried in mitochondrial DNA, make the inner ear unusually sensitive to aminoglycosides; the best known is m.1555A>G. The US label says these variants are present in less than 1% of the US population, and that ototoxicity has occurred in some carriers even when their blood levels were within the recommended range. The UK medicines regulator, the MHRA, puts m.1555A>G at 0.2% of the general population and advises anyone with a known variant, or a family history of hearing damage from these antibiotics, to tell their doctor or pharmacist. The 2022 CPIC pharmacogenetics guideline recommends that carriers avoid aminoglycosides unless the severity of infection outweighs the high risk of permanent hearing loss and no safe or effective alternative exists. The MHRA is also clear that urgent treatment should not be delayed for a genetic test. The MT-RNR1 entry covers inheritance and testing.
What monitoring can and cannot catch
The label asks for kidney function and eighth cranial nerve (hearing and balance) function to be closely monitored, for blood levels to be checked where feasible, and for serial hearing tests where feasible, particularly in high-risk patients. It advises adjusting the dose to avoid prolonged peak levels above 12 mcg/mL and trough levels above 2 mcg/mL. The MHRA recommends monitoring kidney and hearing function before, during and after treatment. How those hearing tests are scheduled and graded is explained under ototoxicity monitoring.
Blood-level monitoring does not settle the question on its own. In the 2012 series, levels were measured in 82 patients and were within the recommended range in 59 of them, and dosing followed Australian antibiotic guidelines in under half. A normal level is reassuring about the dose, not proof that the ear is safe.
Gentamicin also reaches the ear by other routes. The 2019 review notes that aminoglycoside ear drops, used when the eardrum has a hole in it, have caused unintended ear damage; see ototoxic ear drops and perforated eardrum.
If you notice symptoms during or after a course
- Tell the treating team the same day about new ringing, roaring, muffled hearing, unsteadiness or a bouncing view. The label treats these as reasons to review the dose. Do not stop or skip doses on your own: the infection being treated may be serious.
- Hearing that drops over hours to three days needs same-day assessment, as described in sudden hearing loss.
- Severe vertigo or loss of balance that will not settle is an emergency: call your local emergency number or go to an emergency department. Gentamicin damage usually shows as unsteadiness rather than spinning, so severe vertigo should not simply be put down to the drug.
- Ask for a hearing and balance assessment afterwards if symptoms persist. Vertigo, dizziness and tinnitus explains these symptoms, and the when to seek care checklist sorts them by urgency.
Gentamicin on purpose: the Ménière's injection
The 2020 US guideline defines Ménière's disease by spontaneous attacks of vertigo lasting 20 minutes to 12 hours, with low- to mid-frequency hearing loss and fluctuating hearing, tinnitus or fullness in the affected ear. When other measures fail, gentamicin can be injected through the eardrum into the middle ear (intratympanic gentamicin). Cochrane describes the aim as partially or completely destroying the balance function of the affected ear.
What the placebo-controlled evidence shows. Cochrane's 2023 review found five randomised trials with 137 participants in total, all comparing gentamicin with placebo or no treatment, and rated all the evidence very low certainty. In one trial, vertigo improved in 16 of 16 people given gentamicin and 0 of 16 given nothing. At more than 12 months, one trial found 12 of 12 improved on gentamicin against 6 of 10 on placebo, and one reported 0 attacks a year on gentamicin against 11 on placebo. The review could not pool results and found no information about harms such as hearing loss. A 2025 review restricted to randomised trials included three and reached the same verdict: gentamicin may reduce vertigo, but the evidence is very low certainty. The Ménière's article sets this against Cochrane's other Ménière's reviews.
Broader reviews that also count non-randomised studies read more warmly. A 2026 umbrella review of 22 systematic reviews found intratympanic gentamicin had the highest vertigo control rate of the treatments it assessed, 89%, with a 23% rate of people reporting reduced hearing, and noted that the evidence behind it is low quality.
Gentamicin or a steroid injection?
The practical comparison is with intratympanic steroids, which do not destroy balance function. In a 2016 double-blind trial in London and Leicester, 60 adults with Ménière's in one ear that had not responded to other treatment received two injections of either gentamicin or methylprednisolone, two weeks apart. Over the final 6 months of 2 years' follow-up, vertigo attacks had fallen by 87% with gentamicin and 90% with methylprednisolone, with no significant difference. More people were given extra injections after the steroid (15 against 8), and both drugs were well tolerated. When 46 of the 60 were surveyed after an average of 70.8 months, attacks were down by 95% in both groups, with no significant difference on any measure, including a tinnitus questionnaire.
Pooled studies lean slightly the other way. A 2024 meta-analysis of 12 studies and 694 patients found better vertigo control with gentamicin overall (risk ratio 1.36) and at 6 months, but no significant difference at 12 months, and the change in average hearing threshold favoured steroids by 4.41 dB. Its authors caution that the vertigo results varied widely between studies.
How much hearing is at risk
Hearing loss is the recognised cost of the gentamicin injection, and how it is given seems to matter. A 2004 meta-analysis compared five dosing methods. Doses several times a day were linked to significantly more overall hearing loss than the other methods, 34.7%, while weekly injections trended towards less, 13.1%. Rates of profound hearing loss did not differ between methods. Giving doses until balance symptoms, a change in vertigo or hearing loss appeared gave the best complete vertigo control, 81.7%. A 2018 review concluded that injections no more often than weekly, or monthly as needed, give the same vertigo control with better hearing preservation. In a small Dutch study, hearing worsened more in the low frequencies than the high ones after the injection, and speech understanding changed meaningfully in 50% of people.
What happens to tinnitus after the injection
Tinnitus is not what intratympanic gentamicin is for, and the evidence on what happens to it is thin. A 2022 evidence summary, drawing on 13 systematic reviews and 3 randomised trials, concluded that it may improve vertigo control and may make little or no difference to tinnitus, on low-certainty evidence. In a 2002 study of 25 patients, tinnitus decreased in four (16%) and disappeared in three (12%), with no link to the amount of gentamicin given. The small Dutch study above reported less tinnitus after treatment. A 2024 Indian trial of 40 people with good hearing found no significant difference between a single gentamicin dose and four methylprednisolone injections on the Tinnitus Handicap Inventory up to 24 months.
Questions worth asking
- Before an intravenous course: is a baseline hearing test possible, is there a family history of hearing loss after antibiotics, and would an MT-RNR1 test change anything if treatment can wait?
- During it: who do I tell if my hearing, ringing or balance changes, and how quickly will they review the dose?
- Before a Ménière's injection: what is my hearing in that ear now, would a steroid injection be tried first, how often will doses be given, and how will my balance be rehabilitated afterwards?
The medication checker can help you prepare questions about other drugs you take.