“Ototoxicity is the pharmacological adverse reaction affecting the inner ear or auditory nerve, characterized by cochlear or vestibular function.” There are a variety of medications used for therapeutic purposes in fighting cancer and life-threatening infectious diseases that lead to inner ear damage. The symptoms of ototoxicity can include tinnitus, dizziness, and hearing loss along with difficulty discriminating speech in noise, hyperacusis, and aural fullness. Not all drugs have the same impact on the inner ear; therefore, the effects of ototoxicity can be temporary but often permanent, can happen rapidly or develop gradually, and one can experience a single symptom or several otic symptoms simultaneously. Ototoxic hearing loss is not a life-threatening condition; however, it can have a negative impact on communication and quality of life.
There are over 200 prescription and OTC medications that are potentially ototoxic (see table below). However, the most well-established categories of drugs commonly associated with permanent irreversible damage to hearing and/or balance are antineoplastic agents such as cisplatin, and aminoglycoside antibiotics such as gentamicin, tobramycin, and amikacin.
Early identification is crucial in ototoxic hearing loss considering it can be undetected until significant communication difficulties occur. This indicates the deterioration has reached the frequencies necessary for speech discrimination. Ototoxicity begins at the basal end of the cochlea initially affecting the high frequencies so as the damage progresses to the middle/apical end of the cochlea. The communication difficulties are noticeable, and the permanent damage has taken place. The goal in managing ototoxicity is 1) to prevent or minimize communication impairment and identify if that has occurred so that change in the drug regimen can be considered and 2) determine audiologic intervention and develop necessary aural rehabilitation measures.
The most valuable indicator in identifying ototoxic hearing loss is by detecting changes in pure tone thresholds directly using serial audiograms, particularly when ultra-high frequency thresholds are included. There is no standardized protocol per ASHA and AAA for ototoxic monitoring; however, performing audiometric tests that are most sensitive to the damage in the high frequency region that provides the earliest detection includes pure tone thresholds especially ultra-high frequency audiometry, DPOAE’s, and ABR.
Initially, ototoxic monitoring programs involve a baseline evaluation prior to or within the first 24 hours after the administration of chemotherapeutic drugs and no more than 72 hours after the administration of aminoglycoside antibiotics. A follow up check on pure tone thresholds within 24 hours is helpful to assess reliability of patient responses. The following table is a sample of an ototoxic monitoring protocol.
It is recommended by both ASHA and AAA that non-behavioral measures of auditory function are deemed necessary during baseline evaluations due to the possibility of incapacitation and the inability to provide reliable behavioral thresholds during treatment. ASHA recommends evaluations to be done at one month and 3 months following conclusion of ototoxic therapy and a thorough audiologic evaluation at 6 months post-therapy.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5894487/ (J Audiol Otol. 2018 Apr; 22(2):59-68.)