DRUG-INDUCED OTOTOXICITY

What is drug Induced Ototoxicity?

• Drug-Induced ototoxicity can affect hearing (auditory or cochlear function0, balance (vestibular function) depending on the drug.
• Drugs of almost every class have been reported to produce tinnitus (sounds in ear), as have placebos.

The following agents are associated with measurable changes in hearing or vestibular defect when administered systemically.

1. AMINOGLYCOSIDES:

• Aminoglycosides antibiotics can cause cochlear or vestibular toxicities.
• Cochlear toxicity: occurs as progressive hear loss, starting with highest tones and advancing to lower tones. Thus, considerable damage can occur before the patient recognizes it.
• Symptoms of Vestibular damage: include;

1.  Dizziness
2. Vertigo
3. Ataxia

• Both forms of ototoxicity are bilateral and potentially reversible, but permanent damage is common and can progress even after discontinuation of aminoglycosides.
• Clinically detectable ototoxicity in as many as 5% patients.
• Most aminoglycosides-induced ototoxicity is associated with parenteral therapy but has also been associated with topical oral and irrigation use of these of these drugs, especially Neomycin.
• Possible predisposing factors: 

1. Decreased renal function.
2. Long duration of therapy
3. Large total damage
4. Plasma level above therapeutic range
5. Concurrent use of ototoxic drugs
6. Dehydration
7. Old age
8. Genetic susceptibility to aminoglycoside-induced ototoxicity

2. HETEROCYCLIC ANTIDEPRESSANTS:

• The presence of Tricyclic Antidepressants-associated tinnitus is associated to be 1%
• Tinnitus can subside (occur) despite continuous therapy.

3.CHLORQUINE:

• Nerve deafness is rare but consistent feature of chloroquine therapy.
• Its onset is usually delayed and is thought of as irreversible. A partly reversible case and a case resulting from 1g have also been reported.

4.DIURETICS (LOOP DIURETICS):

• Rapid onset hearing loss occurs at high dose, IV administration of Furosemide.
• Gradual onset is with Ethacrynic acid.
• Renal failure is usually the predisposing factor, but only renal failure patients are likely to receive large IV dose.
• Co-administration of Aminoglycoside antibiotics often result in increased ototoxicity.
• Permanent hearing loss has been reported with Ethacrynic acid and Furosemide.
• Bumetanide or Torsemide produce less ototoxicity than Ethacrynic acid and Furosemide.

5.NON-STEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDs):

• Although not as common as Salicylates, NSAIDs have been associated with hearing impairment and deafness, including some cases of permanent damage.
• Tinnitus and vestibular dysfunction are also reported.