Ototoxicity

By Hannah Prather, Au.D., CCC-A, F/AAA

Ototoxicity refers to the meaning that something is toxic to the ear. More specifically, something being toxic to the cochlea (the inner ear) and the auditory nerve. Sometimes, ototoxicity can even affect the vestibular (balance) portion of the auditory nerve as well. Being exposed to an ototoxic agent can cause hearing loss and/or balance problems. This can be exacerbated by genetic factors and environmental factors.

Ototoxic agents can most commonly be found in certain types of medications. They are listed below:

-Aspirin (high levels)

-Quinine

-Loop Diuretics (temporary hearing loss that is typically reversible once the medications are stopped)

-Aminoglycoside Antibiotics such as: amikacin, netilmicin, dihydrostreptomycin, ribostamycin, gentamicin, streptomycin, kanamycin, tobramycin, neomycin.

-Antineoplastics (anti-cancer drugs) such as: cisplatin and carboplatin.

If taken together, loop diuretics and aminoglycoside antibiotics have been found to increase the probability of having damage to the inner ear. The risk of ototoxicity grows even more so when the person is taking these drugs for extended periods of time, has inadequate kidney function, or has a confounding genetic component.

Finally, environmental factors such as butyl nitrite, mercury, carbon disulfide, styrene, carbon monoxide, tin, hexane, toluene, lead, trichloroethylene, manganese and xylene can cause damage to the cochlea and the auditory and vestibular nerves. This type of damage to the inner ear is most often considered permanent damage, and it cannot be reversed.

In a normal healthy inner ear, there are tiny hair cells that respond to different levels of stimuli. These hair cells then send that signal to the brain for the brain to decode what has been heard. The brain is able to make sense of these signals in order to appropriately interpret sounds and speech. In the result of an ototoxic incident, these hair cells become bent. When the hair cells are bent, they are not able to stand up straight to receive the incoming signals. The further that they become bent, the louder the signal will have to become in order for the hair cell to be excited by it. This typically means that the hearing loss has progressed significantly by the ototoxic agent. The damage to the inner ear and auditory nerves usually occurs when the ototoxic agent passes into the cochlea or the nerves via the bloodstream.

In typical Audiological practices, a patient’s hearing status can be tracked and monitored for any changes by completing repeat audiological evaluations. Ideally (but not always), we like to have a baseline audiogram. This is an audiogram or hearing test from a person who has yet to be treated with the above medications. This gives us information about the person’s hearing status prior to taking these types of drugs. If a person begins taking medications that are potentially ototoxic, they can return to clinic for repeat audiological testing to look for changes on the audiogram. This will show if the ototoxic agent has affected the cochlea, auditory nerve, and inner hair cells.

In order to prevent this type of hearing/balance loss from occurring, limited doses of medications can be used alongside monitoring through audiological evaluations. This does not always prevent ototoxicity from occurring, but it can limit the amount of damage that can occur. However, sometimes the reason for taking the ototoxic drug is more important (i.e., treating cancer or another illness) than preserving auditory function. This is usually determined by the physician ordering the medications.

If hearing loss or a loss of balance function occurs from taking ototoxic medications, hearing aids can typically help treat hearing loss. This can be best determined by an audiologist who is completing the audiological testing. Physical therapy can also be completed to help patients restore their balance.

If you have any questions or concerns about a medication you have taken or are currently taking and its possible ototoxic effects, please speak with your doctor or you can contact one of our Audiologists. We would be happy to help you out.