Various drugs used for therapeutic treatment have the potential side effects of causing damage to the inner ear structures.

If the damage progresses, functional hearing impairment and/or balance, with tinnitus is a common complaint.

The revealed impairment can be either permanent or temporary and either unilateral of bilateral in nature.

The severity of a patient’s health condition may override the concern for ototoxic side effects in medical management. However, one should always be aware of the “quality of life”, and the importance of maintaining functional hearing cannot be overemphasized.

Almost every major category of medications contains drugs that can be ototoxic.

Substances of abuse/excess such as alcohol, marijuana, and tobacco can be toxic to the auditory system.

Heavy metals and chemical solvents can also be ototoxic.

Aminoglycoside Antibiotics

All aminoglycosides are ototoxic to some degree. Streptomycin, first used in the successful treatment of tuberculosis, was also found to be quite ototoxic.

Aminoglycoside Antibiotics

Others found to be ototoxic include:

1. Gentamicin

2. Tobramycin

3. Amikacin

4. Netilmicin

5. Kanamycin

6. Neomycin

Aminoglycoside Antibiotics

Streptomycin and Gentamicin are often used to ablate inner ear structures for the relief of Meniere's syndrome symptoms.

Aminoglycoside Antibiotics

Netilmicin and neomycin may be the least ototoxic.

Aminoglycoside Antibiotics

Damage caused by them begins at the basal end of the cochlea and progresses toward the apex.

The concentration of them will remain high within the perilymph fluid, long after the concentration within the blood has diminished.

Cancer Chemotherapeutics

There are significant potentials for ototoxicity among these drugs. They include:

1. Cisplatin

2. Carboplatin

3. Nitrogen mustard

4. Alpha-Difluoromethylornithine (DFMO)

Cancer Chemotherapeutics

Cisplatin may be the most ototoxic of all.

Its effects also reveal cochlear damage beginning at the basal end (high frequency).

Carboplatin is a second generation of Cisplatin and was designed to create less side-effects however, ototoxicity has been reported with its use.

Cancer Chemotherapeutics

Chemoprotective agents have been designed to reduce the side-effects of anti-tumor drugs. Research into these medications involves audiologists who use standardized measures to monitor success or failure.

Loop Diuretics

The most common ones of concern are: furosemide and ethacrynic acid.

Loop Diuretics

By themselves, they usually only create a temporary threshold shift; however, when used with aminoglycosides permanent cochlear damage may result.

Other commonly used medications which generally result in temporary hearing loss are:

Salicylates (aspirin is most common)

Propionic acid (ibuprofen is most common)

Quinine (irreversible HL may result when high dosages are used)

There are several factors which exacerbate or increase the hearing loss effects of ototoxic drugs. Such as:

Excessive noise exposure

Drug interactions

Opportunistic /physiologic susceptibility

Pre-existing hearing loss or vestibular disorder.

Audiometry & Ototoxicity monitoring

Most ototoxic drugs compromise the basal end (high frequency) area of the cochlea.

A high frequency baseline audiogram is recommended before beginning the use of these ototoxic drugs.

Audiometry & Ototoxic monitoring

This monitoring generally involves frequencies above 4K, using high frequency audiometers.

Audiometry & Ototoxic monitoring

Ideally, the highest five frequencies which the patient responds, are used as the baseline for future hearing level measurements.

For example: 6K, 8K, 12K, 14K, 16K.

Audiometry & Ototoxic monitoring

When the threshold at any frequency shifts by more than ten decibels, ototoxic effects may be present. When adjacent frequencies are involved, most certainly effects have occurred.

When a twenty decibel shift occurs at any single frequency, ototoxicity effects are present.

Audiometry & Ototoxic monitoring

For Aminoglycoside treated patients, audiometric testing should be done every two to four days during treatment.

For Cisplatin patients, audiometric testing should be done within twenty-four hours of each treatment.

Audiometry & Ototoxic monitoring

Follow-up audiometric testing should be scheduled up to thirty days after Ototoxic treatments have been discontinued.

Audiometric monitoring can be very useful in the successful treatment and best practices outcomes for patient healthcare.