This document discusses ototoxicity, or damage to the inner ear from chemicals. It defines ototoxicity and lists common ototoxic drugs like aminoglycosides, diuretics, antimalarials, and anticancer drugs. High risk groups include those with impaired kidney function, the elderly, and those receiving multiple ototoxic medications. Various drugs are described in more detail regarding their mechanisms and effects on the inner ear. The document also discusses topical ear drops, investigations for ototoxicity, and management strategies like discontinuing ototoxic drugs and using hearing aids.

1. Ototoxicity
a silent hazard

2. Definition
– Damage to the cochlea or vestibular
apparatus from exposure to a chemical
source.
– The sources may include the drugs consumed
by the patient on therapeutic or non
therapeutic purposes and also the compounds
present in the environment.

3. Ototoxic drugs
- Aminoglycosides
- Diuretics
- Antimalarials
- Anticancer drugs
- Analgesics
- Miscellaneous

4. High risk groups
- Patients having impaired renal function.
- Elderly patients(age above 65 yrs).
- Patients simultaneously receiving other ototoxic
drugs [aminoglycosides when concomitantly
used with diuretics have synergistic ototoxicity].
- Patients who have genetic susceptibility to these
group of drugs.
- Patients under prolonged treatment.

5. Aminoglycosides
- Streptomycin, Gentamicin, Tobramycin, Neomyc
in and Kanamycin.
- Cochlear toxicity:
Neomycin, Kanamycin, Amikacin.
- Vestibular toxicity: Gentamicin, Streptomycin
- Pathogenesis: Selectively destroy outer hair
cells, they even destroy inner hair cells.
- Symptoms: hearing loss, tinnitus, vertigo

6. Normal inner ear hair cells Damaged inner ear hair cells

7. Diuretics
- Furosemide and Ethacrynic acid (loop diuretics)
- Known to cause edema and cystic changes in
stria vascularis of cochlear duct.
- The edema is caused due to blockage of Na+ &
Cl- ions transport.
- Effect: mostly reversible but permanent damage
may occur.

8. Antimalarials
- Quinine & Chloroquine
- Ototoxic effect is due to vasoconstriction in the
small vessels of the cochlea and stria vascularis.
- The effect is reversible which generally appears
on prolonged medication, but deafness is
permanent with chloroquine.
- Congenital deafness and hypoplasia of cochlea
have been reported in children whose mothers
received these drugs during pregnancy(1st
trimester).

9. Anticancer drugs
- Nitrogen
mustards(Cyclophosphamide, Ifosfamide), Cispla
tin, Carboplatin can cause cochlear damage.
- Ototoxic effect is due to outer hair cell
degeneration leading to high frequency sensory
neural hearing loss.

10. Analgesics
- NSAIDS like Salicylates, Indomethacin, Phenyl
butazone, Ibuprofen.
- Ototoxic effect is reversible and is due to
interference at enzymatic level.
- No structural damage hence normal
histology(no hair cell loss)
- Site of lesion testing indicates cochlear
involvement.
- Symptoms: tinnitus and b/l hearing loss
particularly affecting higher frequencies.

11. Miscellaneous
- Desferrioxamine: Iron chelating substance.
- It causes high frequency sensory neural hearing
loss.The effect is permanent but rarely reversible.
- Cases of deafness have been reported with
Erythromycin, Ampicillin, Propanalol, Propyl
thiouracil, Phenytoin, Barbiturates, Hexadimethi
ne bromide, Dantrolene, OCPs.
- Alcohol, tobacco and marijuana also cause
damage to inner ear.

12. Chemicals classes:
- Gas(Carbon monoxide)
- Heavy metals(lead, arsenic, mercury)
- Organic solvents(carbon disulfide, styrene, xylene
and toluene).

13. Topical drugs
- Topical ear drops used in the treatment of otitis
externa may be absorbed from the round and
oval windows into the fluids of inner ear leading
to ototoxicity.
- Chlorhexidine which was used in the
preparartion of ear canal before surgery has also
been blamed for such deafness.

14. Investigations
- Monitoring drug concentrations in the body.
- PTA
- Caloric test
- Electrocochleography
- Oto-acoustic emission
- BERA(brain stem evoked response audiometry)

15. Management
- Early recognition and discontinuation of drugs.
- Hearing aid in cases of severe hearing loss.
- Tinnitus treated by mild hypnotics.
- Disequilibrium should be treated with
reassurance and regular physiotherapy including
vestibular exercises, wearing of soft thick padded
shoes, avoidance of walking in darkness and
unnecessary head movement.

16. Abhilash