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.
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
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.
