Certain medications like aminoglycoside antibiotics and chemotherapy drugs can cause permanent hearing loss or damage to balance functions. Audiometric monitoring of high frequencies above 8 kHz is the most effective way to detect this ototoxicity early. High frequencies are affected first, which can later degrade speech understanding if the hearing loss spreads to lower frequencies that are important for speech. Early detection allows for potential intervention to minimize ototoxic impacts.

1. OTOTOXICITY
Dr. Ghulam Saqulain
Head Of Department of ENT
Capital Hospital

2. Close to 200 prescription and OTC medications have ototoxic
potential.
“Drug-induced hearing loss accounts for most cases of preventable
hearing loss worldwide”

3. Two categories of medications that have the
greatest potential for permanent changes in
hearing and or balance are:
 aminoglycosides and
 anti-neoplastic agents.
Others Are:
 Diuretic- furosemide, ethacrynic acid
 Salicylate-aspirin
 antimalarial drug- quinine

4. X

5. X

6. Clinical characteristics of ototoxic deafness
 Bilateral hearing loss
 Hearing loss happens at high frequency
 Reversible or progressive
 With tinnitus, vertigo

7. Audiometric Monitoring for
Ototoxicity
 The only way to detect ototoxicity is by
audiometric monitoring of extended high
frequencies, above 8 KHz.

8. Pathophysiology of Ototoxicity
 Hair cells in the inner ear are primarily
affected.
 In the vestibular system type I hair cells of the
crista of the semi-circular canals are targeted
X

9. Semicircular canals:
Superior
Posterior
Lateral
Utricle
Saccule
Cochlea
Stapes
Vestibulocochlear
nerve

10. X

11. X

12. Incidence of aminoglycoside
Ototoxicity
 Incidence
 ranges 20-33% for commonly used
aminoglycosides while
 balance is affected in 18% of cases.

13. Risk Factors
 Long term treatment i.e. TB patients
 Impaired renal function – increases drug half-
life
 Concomitant use of loop diuretics
 Genetic – mitochondrial mutations (1555
mutation)

14. Aminoglycoside Ototoxicity
 Streptomycin was the first aminoglycosides
antibiotic and the first drug effective against
TB.
 Discovered by Selman Waksman et al in
1944.
 Adverse side effects on the kidney and inner
ear (vestibular toxicity) were reported in 1945

15. Aminoglycoside Ototoxicity
 In the last 20 years the use of
aminoglycosides has declined in industrial
societies
 In developing countries, their effectiveness
and low cost make them popular.
 They are often sold OTC and are the most
commonly used antibiotics worldwide.
X

16. Aminoglycoside Ototoxicity
 With the resurgence of drug resistant TB,
there is renewed interest in aminoglycosides
specifically streptomycin and amikacin/
kanamycin as part of the World Health
Organization recommended multi drug
regimen.
X

17. Effect of Aminoglycosides on
Auditory/Vestibular Functions
 Studies of human temporal bones and
experimental animals show inner ear hair
cells are the first to be affected followed by
outer hair cells..
 Outer hair cells are targeted in the cochlea
extending from base to apex.
 Results in high frequency hearing loss which
can extend to frequencies important to
understanding speech.

18.  In the vestibular system, its primary effect is loss
of vestibular hair cells in the semi circular canals
and Utricular macula.
 This leads to oscillopsia resulting in postural
instability and risk of fall.
 It was once believed that maintaining peak and
trough serum levels of a drug would mitigate
ototoxic effects.
 Current evidence shows this not to be the case
at least for vestibular toxicity.

19.  Gentamycin and streptomycin are considered
more vestibulotoxic.
 Amikacin and Neomycin are considered more
cochleo-toxic.

20. Pharmokinetics
 Presence of the drug does not necessarily
cause toxicity
 Concentration of the drug in the inner ear
does not exceed the serum level
 Half life in cochlear tissue has been
measured to exceed one month
 Traces can be detected up to 6 months
following the end of treatment.

21. Mechanisms of Aminoglycoside
Ototoxicity
 Reactive Oxygen Species (ROS) formation appears to
be key.
 Reactive oxygen species (ROS) are chemically reactive
molecules containing oxygen. Examples
include oxygen ions and peroxides. ROS are formed as
a natural byproduct of the normal metabolism of oxygen
 Depletion of anti oxidant Glutathione (GSH) enhances
ototoxicity while dietary supplementation inhibits toxicity.

22. Is Aminoglycoside ototoxicity
preventable?
 Medications showing promise are d-
methiomine and salicylate.
 Two issues need to be solved before
protective treatment can be considered.
 Effective drug levels must be maintained.
 Drug must not interfere with the anti-bacterial
activity of the aminoglycosides.
X

23.  One clinical study found aspirin was
protective reducing incidence of hearing loss
by 75%.
Sha, S. H. , Qui, J. H. & Schacht, J. (2006) Aspirin to prevent gentamicin-induced
hearing loss. New England Journal of Medicine, 354, 1856-7.
X

24. Chemotheraputic Agents &
Ototoxicity - Cisplatin
 Introduced in the 1970s and is effective
against germ cell, ovarian, endometrial,
cervical, urothelial, head and neck, brain and
lung cancers. X
 Highest ototoxic potential and is the most
ototoxic drug in clinical use.
 Symptoms of ototoxicity begin with tinnitus
and high frequency hearing loss.

25.  Incidence of hearing loss has been reported
at 11-91% with an overall incidence of 69%.
 In patients with head and neck cancer treated
with Cisplatin, about 50% develop hearing
loss.

26. Risk Factors for Cisplatin
Ototoxicity
 Intravenous bolus administration or high
cumulative dose
 Young children, under 5 years, or older > 46
years
 Renal insufficiency
 Prior cranial irradiation
 Co-administration of vincristin
X

27.  The best predictor of cisplatin ototoxicity is
cumulative dose.
 The critical dose is 3-4 mg/Kg body weight.
 Ototoxicity increased dramatically when the
total cumulative dose exceeds 400 mg/m2
X

28. Characteristics of Cisplatin
Ototoxicity
 Bilateral and permanent. High frequencies
affected first.
 It can occur suddenly. Speech discrimination
may be markedly affected.

29. Mechanisms of Cisplatin
Ototoxicity
 Hearing loss affected by free radical
formation and anti-oxidant inhibition.
 Formation of reactive oxygen radicals
produces glutathione depletion in the cochlea
and lipid peroxidation.
 Induced apoptosis in hair cells causing
permanent hearing loss.
X

30. Carboplatin
 Introduced due to its lower nephrotoxicity
than cisplatin.
 It is used to treat small cell lung cancer,
ovarian and head and neck cancers.
 carboplatin is less toxic than cisplatin but
higher doses of carboplatin are used
increasing ototoxicity
X

31. OTOTOXIC MONITORING
 Ototoxicity is determined by establishing
baseline hearing test data ideally prior to
treatment including testing at high
frequencies.
 Results are compared to serial audiograms
allowing the patient to serve as their own
control.

32.  The highest frequencies measuring 100 dB or
less are monitored with testing ideally
occurring just prior to each chemotherapeutic
dose
 Monitoring 1-2 times per week for patients
receiving ototoxic antibiotics.
 Post treatment evaluations are conducted as
soon as possible after dispensing the drug
and repeated at 1, 3 and 6 month post
treatment.

33.  The customized test protocol is called the
Sensitive Range for Ototoxicity, or SRO and
differs for each patient.
 It consists of the highest frequencies with
thresholds 100 dB or better followed by the
next six lower frequencies.
 The SRO is established during baseline
testing prior to ototoxic drug administration.

34. Summary
 Audiometric monitoring using the patient’s
own extended high frequency thresholds as
a control, is the most sensitive method to
detect ototoxicity.
 The test is easily tolerated
 High frequency hearing is affected first
 Speech perception can degrade if hearing
loss extends below 8KHz.