Various drugs used for therapeutictreatment have the potential side effectsof causing damage to the inner earstructures.
If the damage progresses, functional hearing impairment and/or balance, with tinnitus is a common complaint. The revealed impairment can be either permanent or temporary and either unilateral of bilateral in nature.
The severity of a patient’s healthcondition may override the concern forototoxic side effects in medicalmanagement. However, one shouldalways be aware of the “quality of life”,and the importance of maintainingfunctional hearing cannot beoveremphasized.
Almost every major category of medications contains drugs that can be ototoxic. Substances of abuse/excess such as alcohol, marijuana, and tobacco can be toxic to the auditory system. Heavy metals and chemical solvents can also be ototoxic.
Aminoglycoside AntibioticsAll aminoglycosides are ototoxic to somedegree. Streptomycin, first used in thesuccessful treatment of tuberculosis, wasalso found to be quite ototoxic.
Aminoglycoside AntibioticsOthers found to be ototoxic include:1. Gentamicin2. Tobramycin3. Amikacin4. Netilmicin5. Kanamycin6. Neomycin
Aminoglycoside AntibioticsStreptomycin and Gentamicin are oftenused to ablate inner ear structures forthe relief of Menieres syndromesymptoms.
Aminoglycoside AntibioticsNetilmicin and neomycin may be theleast ototoxic.
Aminoglycoside Antibiotics Damage caused by them begins at the basal end of the cochlea and progresses toward the apex. The concentration of them will remain high within the perilymph fluid, long after the concentration within the blood has diminished.
Cancer ChemotherapeuticsThere are significant potentials for ototoxicityamong these drugs. They include:1. Cisplatin2. Carboplatin3. Nitrogen mustard4. Alpha-Difluoromethylornithine (DFMO)
Cancer ChemotherapeuticsCisplatin may be the most ototoxic of all.Its effects also reveal cochlear damagebeginning at the basal end (high frequency).Carboplatin is a second generation ofCisplatin and was designed to create lessside-effects however, ototoxicity has beenreported with its use.
Cancer ChemotherapeuticsChemoprotective agents have been designedto reduce the side-effects of anti-tumor drugs.Research into these medications involvesaudiologists who use standardized measuresto monitor success or failure.
Loop DiureticsThe most common ones of concernare: furosemide and ethacrynicacid.
Loop DiureticsBy themselves, they usually only create atemporary threshold shift; however,when used with aminoglycosidespermanent cochlear damage may result.
Other commonly used medicationswhich generally result in temporaryhearing loss are: Salicylates (aspirin is most common) Propionic acid (ibuprofen is most common) Quinine (irreversible HL may result when high dosages are used)
There are several factors whichexacerbate or increase the hearing losseffects of ototoxic drugs. Such as: Excessive noise exposure Drug interactions Opportunistic /physiologic susceptibility Pre-existing hearing loss or vestibular disorder.
Audiometry & Ototoxicity monitoring Most ototoxic drugs compromise the basal end (high frequency) area of the cochlea. A high frequency baseline audiogram is recommended before beginning the use of these ototoxic drugs.
Audiometry & Ototoxic monitoringThis monitoring generally involvesfrequencies above 4K, using highfrequency audiometers.
Audiometry & Ototoxic monitoringIdeally, the highest five frequencieswhich the patient responds, are used asthe baseline for future hearing levelmeasurements.For example: 6K, 8K, 12K, 14K, 16K.
Audiometry & Ototoxic monitoring When the threshold at any frequency shifts by more than ten decibels, ototoxic effects may be present. When adjacent frequencies are involved, most certainly effects have occurred. When a twenty decibel shift occurs at any single frequency, ototoxicity effects are present.
Audiometry & Ototoxic monitoring For Aminoglycoside treated patients, audiometric testing should be done every two to four days during treatment. For Cisplatin patients, audiometric testing should be done within twenty-four hours of each treatment.
Audiometry & Ototoxic monitoring Follow-up audiometric testing should be scheduled up to thirty days after Ototoxic treatments have been discontinued. Audiometric monitoring can be very useful in the successful treatment and best practices outcomes for patient healthcare.