Medications That Can Cause Ototoxicity
Last updated: 05/31/2006
Hearing, one of the five senses, is very important. It allows a person to detect sounds and has a role in a person's sense of balance. Without hearing, a person's interaction with his everyday environment is limited. Medications that are prescribed to a person can have a negative effect on the person's sense of hearing by various mechanisms. The incidence of ototoxicity is unknown; however, it has been reported that approximately 130 medications may produce ototoxicity.
The main areas of the ear where ototoxicity occurs are the cochlea, the vestibulum, and the stria vascularis. The cochlea is where sound vibrations are converted into nerve impulses. When a medication affects the cochlea, hearing loss is produced. The level of hearing loss varies. Sometimes, tinnitus is associated with cochlear damage.
The vestibulum is the part of the ear that controls balance. When a medication affects this part of the ear, balance-related problems may occur. If a patient reports that he feels like he is spinning and nauseated, the medication may caused toxicity at the vestibular level.
Lastly, the stria vascularis produces endolymph in the cochlea. Too much endolymph can cause Meniere's syndrome.
Because most ototoxic medications are renally eliminated, renal insufficiency can put a person at a higher risk for ototoxicity. Taking two medications that cause ototoxicity may have an additive effect on risk. It is important to remember that the risk of ototoxicity depends on many factors, including the dose, the age of the patient, dehydration, the length of time that a medication is given, and the patient's medical history.
Medications that can cause ototoxicity include aminoglycosides, topical otic preparations, loop diuretics, antineoplastics, salicylates and quinine. Aminoglycosides like gentamicin and streptomycin are toxic to the vestibula while other amino-glycosides like amikacin affect the cochleae. Damage results from free radical production.
Topical otic preparations may also cause ototoxicity. They are most dangerous when the person has a perforation in the eardrum. Vestibular and/or cochlear damage may occur because the medication (e.g. polymyxin B/neomycin containing product) may reach even higher levels than normal and cause toxicity.
Another class of medications that can have a negative effect on the ear is loop diuretics such as furosemide and bumetanide. The potassium gradient of the stria vascularis and the electrical potential of the endocochlear structure are affected by loop diuretics. As a result, tinnitus and hearing loss occur. Toxicity, however, is dose related and sometimes reversible.
Antineoplastics such as cisplatin generate free rad-cals in the inner ear that can damage the cochlea and the stria vascularis. The hearing loss is typically bilateral and symmetrical. Currently there are no compounds that can be given with anti-neoplastics that can help to protect the ear, although investigation in this area is ongoing.
In the case of salicylates, ototoxicity is related to serum concentration. Serum concentrations of salicylates greater than 20 to 50 mg/dL put a patient at a greater risk of hearing loss due to cochlear involvement. Ototoxicity may appear in the form of tinnitus. In most cases, the effect of salicylates decreases when the medication is stopped and often resolves within seventy-two hours.
With quinine, a twenty percent risk of hearing loss occurs with doses from 200 to 300 mg over a period of time. Quinine has the potential to cause hearing loss, tinnitus, or vertigo, of which the hearing loss is irreversible.
It is important to realize the possible ototoxic effect of these medications. While many medications can produce adverse reactions, one must weigh the risks versus benefits of the medication and monitor for possible events, especially with long-term use or high doses of medications.