Residency · Residency · Otolaryngology
Ototoxicity and Hearing Conservation
Introduction
Ototoxicity refers to the damaging effect of certain medications and chemicals on the inner ear structures, resulting in hearing loss, tinnitus, and/or vestibular dysfunction. With the widespread use of ototoxic agents in clinical practice, the otolaryngologist must be familiar with the common offending drugs, monitoring protocols, and strategies for hearing conservation. Additionally, noise-induced hearing loss (NIHL) is a major preventable cause of sensorineural hearing loss.
Anatomy of Ototoxic Injury
Cochlear Toxicity
Primarily targets the outer hair cells (OHCs) of the organ of Corti. Damage begins at the basal turn (high frequencies) and progresses apically. Results in high-frequency sensorineural hearing loss initially. Severe toxicity involves inner hair cells and spiral ganglion neurons.
Vestibular Toxicity
Targets Type I hair cells of the vestibular neuroepithelium. Affects the cristae of the semicircular canals and maculae of the utricle and saccule. Results in oscillopsia, disequilibrium, and bilateral vestibular hypofunction.
Stria Vascularis Toxicity
Loop diuretics primarily affect the stria vascularis, disrupting the endocochlear potential. Usually reversible upon drug discontinuation.
Common Ototoxic Medications
| Drug Class | Key Agents | Primary Toxicity | Reversibility |
|---|---|---|---|
| Aminoglycosides | Gentamicin, amikacin, neomycin, streptomycin | Cochlear (amikacin, neomycin) or vestibular (gentamicin, streptomycin) | Irreversible |
| Platinum agents | Cisplatin, carboplatin | Cochlear (OHC, stria vascularis) | Irreversible; cumulative |
| Loop diuretics | Furosemide, ethacrynic acid | Stria vascularis | Usually reversible |
| Salicylates | Aspirin (high dose) | OHC (prestin inhibition) | Reversible |
| Macrolides | Erythromycin (high IV dose) | Cochlear | Reversible |
Aminoglycoside Antibiotics
Gentamicin, tobramycin, amikacin, streptomycin, neomycin. Mechanism: generate reactive oxygen species (ROS) in hair cells; enter through mechanoelectric transduction channels. Gentamicin: preferentially vestibulotoxic. Amikacin and neomycin: preferentially cochleotoxic. Streptomycin: primarily vestibulotoxic (exploited therapeutically for Meniere disease). Risk factors: renal impairment, prolonged use, concurrent ototoxic drugs, genetic susceptibility (MT-RNR1 mitochondrial mutation). Damage is dose-dependent and often irreversible.
Cisplatin and Carboplatin
Cisplatin: most ototoxic chemotherapeutic agent; affects the OHCs and stria vascularis. Bilateral, symmetric, high-frequency SNHL; dose-dependent and cumulative. Incidence: 50-80% of patients receiving cisplatin develop some hearing loss. Carboplatin: less ototoxic than cisplatin but still significant, especially in children. Sodium thiosulfate: FDA-approved otoprotectant for cisplatin-related ototoxicity in pediatric patients with localized, non-metastatic solid tumors.
Loop Diuretics
Furosemide, ethacrynic acid, bumetanide. Mechanism: inhibit Na-K-2Cl cotransporter in the stria vascularis; reduce endocochlear potential. Usually reversible with dose reduction or discontinuation. Risk greatly increased with concurrent aminoglycoside use (synergistic ototoxicity).
Salicylates and NSAIDs
Aspirin at high doses (4-8 g/day): tinnitus and bilateral SNHL. Mechanism: inhibits prestin in OHCs, reduces cochlear blood flow. Reversible upon dose reduction.
Other Ototoxic Agents
Quinine and chloroquine: tinnitus, SNHL (usually reversible). Vancomycin: ototoxic at high serum levels, especially with concurrent aminoglycosides. Erythromycin: at high IV doses, reversible SNHL. Vincristine and nitrogen mustard: vestibulotoxic and cochleotoxic.
Ototoxicity Monitoring
Who to Monitor
All patients receiving cisplatin-based chemotherapy. Patients on aminoglycosides for more than 5-7 days (or any duration with renal impairment). Patients on high-dose loop diuretics, especially with concurrent ototoxic medications. Patients reporting new tinnitus or hearing change during ototoxic drug therapy.
Monitoring Protocol (ASHA Guidelines)
Baseline audiogram before initiating ototoxic therapy (within 72 hours of first dose). Serial audiometry during treatment: frequency depends on agent and protocol. Extended high-frequency audiometry (9-20 kHz): earliest changes detected in ultra-high frequencies. OAE (otoacoustic emissions): DPOAE monitoring detects early OHC dysfunction before audiometric changes. Significant ototoxic change: >=20 dB shift at any single frequency, >=10 dB shift at two consecutive frequencies, or loss of response at three consecutive frequencies where responses were previously obtained.
Management of Detected Ototoxicity
Communicate findings to the oncologist/treating physician. Risk-benefit analysis: may modify dosing, switch agents, or accept hearing loss if life-saving treatment. Hearing rehabilitation: hearing aids, cochlear implant for severe bilateral loss. Vestibular rehabilitation for vestibulotoxicity.
Noise-Induced Hearing Loss (NIHL)
Pathophysiology
Excessive noise causes mechanical shear stress and metabolic exhaustion of hair cells. Temporary threshold shift (TTS): recoverable hearing loss after noise exposure. Permanent threshold shift (PTS): irreversible loss from hair cell death. Noise exposure exceeding 85 dB for 8 hours (OSHA action level) is hazardous. Every 3 dB increase halves the safe exposure time (exchange rate). Classic audiometric pattern: 4 kHz notch (dip at 4000 Hz with recovery at 8000 Hz).
Risk Factors
Occupational noise (construction, military, manufacturing, music industry). Recreational noise (firearms, concerts, personal listening devices). Combined exposure with ototoxic chemicals (solvents, heavy metals).
Prevention and Hearing Conservation Programs
Engineering controls: reduce noise at the source. Administrative controls: limit exposure duration, rotate workers. Personal hearing protection: earplugs (NRR 15-30 dB), earmuffs (NRR 20-35 dB). Annual audiometric monitoring for noise-exposed workers (OSHA standard). Education: awareness of hazardous noise levels and proper HPD use.
Emerging Otoprotective Strategies
N-acetylcysteine (NAC): antioxidant; some evidence for protection against noise and cisplatin. D-methionine: antioxidant; Phase III trials for cisplatin otoprotection. Sodium thiosulfate: FDA-approved for cisplatin ototoxicity in pediatric cancers. Dexamethasone intratympanic injection: may mitigate cisplatin ototoxicity. Gene therapy and hair cell regeneration: investigational; targeting Atoh1/Math1 for hair cell regeneration.
Key Clinical Pearls
Ototoxic hearing loss begins at high frequencies and is often not noticed by the patient until speech frequencies are affected. Baseline audiometry before initiating ototoxic therapy is essential and often omitted. Aminoglycoside ototoxicity is often irreversible; the MT-RNR1 mitochondrial mutation confers extreme susceptibility. Cisplatin ototoxicity is cumulative and dose-dependent; monitoring should continue even after treatment ends. The combination of aminoglycosides and loop diuretics is synergistically ototoxic and should be avoided when possible. The 4 kHz notch on audiometry is the hallmark of noise-induced hearing loss and helps distinguish it from presbycusis.
References
- Rybak LP, Mukherjea D, Jajoo S, Ramkumar V. Cisplatin ototoxicity and protection: clinical and experimental studies. Tohoku J Exp Med. 2009;219(3):177-186.
- Fausti SA, Henry JA, Helt WJ, et al. An individualized, sensitive frequency range for early detection of ototoxicity. Ear Hear. 1999;20(6):497-505.
- Basner M, Babisch W, Davis A, et al. Auditory and non-auditory effects of noise on health. Lancet. 2014;383(9925):1325-1332.
- American Speech-Language-Hearing Association. Audiologic management of individuals receiving cochleotoxic drug therapy. ASHA Guidelines. 1994.