Ototoxicity

Ototoxicity ("ear poisoning") is due to drugs or chemicals that damage the inner ear or the vestibulo-cochlear nerve, which sends balance and hearing information from the inner ear to the brain. Ototoxicity can result in temporary or permanent disturbances of hearing, balance, or both.

Many chemicals have ototoxic potential, including over-the-counter drugs, prescription medications, and environmental chemicals. If you are taking any drugs on the advice of your physician, do not stop taking them just because you see them listed below. Speak with your doctor or other health care advisor about your concerns.

Substances that may cause ototoxicity include:

Aminoglycoside antibiotics, including gentamicin, streptomycin, kanamycin, tobramycin, neomycin, amikacin, netilmicin, dihydrostreptomycin, and ribostamycin. All members of this family are well known for their potential to cause permanent ototoxicity. They can enter the inner ear through the blood system, through inhalation, or via diffusion from the middle ear into the inner ear. They enter the blood stream in largest amounts when given intravenously (by IV).

Anti-neoplastics (anti-cancer drugs). Cisplatin is well known to cause hearing loss that is many times massive and permanent. Carboplatin has been implicated as well.

Environmental chemicals, including butyl nitrite, mercury, carbon disulfide, styrene, carbon monoxide, tin, hexane, toluene, lead, trichloroethylene, manganese, and xylene. Most are associated with hearing disturbances that may be permanent; mercury has also been linked to permanent balance problems.

Loop diuretics, including bumetanide (Bumex), ethacrynic acid (Edecrin), furosemide (Lasix), and torsemide (Demadex). These drugs cause ringing in the ears or decreased hearing that reverses when the drug is stopped. Note: Hydrochlorothiazide (HCTZ) and Maxide, diuretics commonly prescribed to people with Meniere's disease or other forms of endolymphatic hydrops, are not loop diuretics.

Aspirin and quinine products. These may cause temporary ototoxicity, particularly tinnitus, but may also reduce hearing.

Symptoms of ototoxicity vary considerably from drug to drug and person to person. They range from mild imbalance to total incapacitation, and from tinnitus to total hearing loss.

A bilateral (two-sided) vestibular loss usually doesn't produce intense vertigo, vomiting, and nystagmus but instead a headache, a feeling of ear fullness, imbalance to the point of being unable to walk, and a bouncing and blurring of vision (oscillopsia). It also produces inability to tolerate head movement, a wide-based gait (walking with the legs farther apart than usual), difficulty walking in the dark, a feeling of unsteadiness and actual unsteadiness while moving, lightheadedness, and severe fatigue. If the damage is severe, symptoms such as oscillopsia and problems with walking in the dark or with the eyes closed are not going to go away.

The diagnosis of ototoxicity is based upon the patient's history, symptoms, and test results. There is no specific test; this makes a positive history for ototoxin exposure crucial to the diagnosis.

At present, there are no treatments that can reverse the damage. Currently available treatments are aimed at reducing the effect of the damage and rehabilitating function. Individuals with hearing loss may be helped with hearing aids, and those with profound bilateral losses have benefited from cochlear implants. In the case of lost balance function, physical therapy is of great value for many individuals. The aim is to help the brain become accustomed to the changed information from the inner ear and to assist the individual in developing other ways to maintain balance.

From VEDA publication F-19, Ototoxicity