Council on Aging Answers 2015 - 44

COUNCIL ON AGING - ORANGE COUNTY

hEALThCARE

Medication-Related Ototoxicity
n Mark D. Coggins, PharmD, CGP, FASCP
Older adults' hearing loss frequently is attributed to
the aging process, but some medications also can cause
damage that can lead to hearing loss, which is formally
termed as ototoxic. Because of the increased incidence of
medication use among older adults, physicians should be
aware of medications that may be considered ototoxic -
having a toxic effect on the ear or its nerve supply.
Causes and Symptoms
Medications and environmental substances that
damage structures within the inner ear or vestibulecochlear nerve are considered ototoxic, with at least 300
medications identified as such. The damage they cause
to hair cells prevents the transmission of sound and motion into electrical impulses the brain can understand.
Symptoms of ototoxicity include tinnitus (ringing in
the ears), hearing loss in one or both ears, dizziness, lack
of movement coordination, unsteady gait, and oscillating or bouncing vision (vertigo). Hearing loss may be
complete or partial, depending on the severity of damage to the hair cells lining the cochlea. Tinnitus, which
often is one of the first symptoms of damage, also may
be described as roaring, clicking, hissing, or buzzing
and may be soft or loud and high or low pitched. Additionally, fall risk can increase for patients who experience dizziness, poor coordination, unsteady gait, or
vertigo.
The progression of ototoxicity may be rapid or appear
months following medication use. In the early stages,
otoxicity may go undiagnosed if hearing loss is minimal or restricted to high-pitched sounds. As exposure
to ototoxic medications increases, resulting damage
can initially affect the ear's ability to comprehend highpitched sounds and them subsequently affect lowerpitched sounds. It is usually when hearing loss affects
the lower speech frequencies that patients notice the
changes, but often this also is the stage by which permanent damage has occurred.
Monitoring
In addition to being aware of symptoms associated
with ototoxicity, clinicians and patients should consider
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Answers Guide 2015

utilizing audiologists, who can perform hearing tests
before, during, and after the administrations of medications to detect the progression of ototoxic hearing loss.
The progression from the loss of high frequency,
high-pitched sounds to low frequency, low-pitched
sounds is important in evaluating hearing loss. Whereas typical hearing tests frequencies only as high as
6,000 to 8,000 Hz, audiologists can perform testing that
evaluates hearing in very high frequencies such as 9,000
to 20,000 Hz possibly allowing for earlier detection of
ototoxic effects.

Drug Accumulation
It is essential for health care providers to understand
the risk factors for ototoxicity, which often lead to drug
accumulation and an increased potential for permanent
hearing loss. These risk factors include medication dose,
therapy duration, cumulative lifetime dose, impaired
kidney function, infusion rate of certain medications
(eg, IV furosemide, aminoglycosides) co-administration
of multiple ototoxic medications (eg, aminoglycosides
with loop diuretics), age, previous exposure to head and
neck radiation (chemotherapeutic agents), genetic susceptibility, and family history of ototoxicity.
Since most ototoxic drugs are eliminated through the
kidneys, the risk of toxicity is increased by renal failure.
When renal function is diminished, doses of ototoxic
medications must be corrected to ensure blood levels remain therapeutic. Routine monitoring of blood levels is
essential to ensure that ototoxic medications, such as the
aminoglycosides, are kept below maximum therapeutic
levels. Keeping these medications within suggested limits often can preserve hearing.
Older adults are at greater risk of ototoxicity because
of several factors that can contribute to drug accumulation in the body, including reduced renal and hepatic
functions, increased potential for polypharmacy and
drug interactions, increased sensitivity to adverse drug
reactions, and decreased metabolism of medications.
Risk vs. Benefit
Before starting patients on a medication known to
be ototoxic, it is important for the healthcare team to
consider the possible effects hearing and /or balance

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Council on Aging Answers 2015

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