|Classification and external resources|
Ototoxicity is the property of being toxic to the ear (oto-), specifically the cochlea or auditory nerve and sometimes the vestibular system, for example, as a side effect of a drug. The effects of ototoxicity can be reversible and temporary, or irreversible and permanent. It has been recognised since the 19th century. There are many well-known ototoxic drugs used in clinical situations, and they are prescribed, despite the risk of hearing disorders, to very serious health conditions. Ototoxic drugs include antibiotics such as gentamicin, loop diuretics such as furosemide and platinum-based chemotherapy agents such as cisplatin. A number of nonsteroidal anti-inflammatory drugs (NSAIDS) have also been shown to be ototoxic. This can result in sensorineural hearing loss, dysequilibrium, or both. Some environmental and occupational chemicals have also been shown to affect the auditory system and interact with noise.
Antibiotics in the aminoglycoside class, such as gentamicin and tobramycin, may produce cochleotoxicity through a poorly understood mechanism. It may result from antibiotic binding to NMDA receptors in the cochlea and damaging neurons through excitotoxicity. Aminoglycoside-induced production of reactive oxygen species may also injure cells of the cochlea. Once-daily dosing and co-administration of N-acetylcysteine may protect against aminoglycoside-induced ototoxicity. The anti-bacterial activity of aminoglycoside compounds is due to inhibition of ribosome function and these compounds similarly inhibit protein synthesis by mitochondrial ribosomes because mitochondria evolved from a bacterial ancestor. Consequently, aminoglycoside effects on production of reactive oxygen species as well as dysregulation of cellular calcium ion homeostasis may result from disruption of mitochondrial function. Ototoxicity of gentamicin can be exploited to treat some individuals with Ménière's disease by destroying the inner ear, which stops the vertigo attacks but causes permanent deafness. Due to the effects on mitochondria, certain inherited mitochondrial disorders result in increased sensitivity to the toxic effects of aminoglycosides.
Macrolide antibiotics, including erythromycin, are associated with reversible ototoxic effects. The underlying mechanism of ototoxicity may be impairment of ion transport in the stria vascularis. Predisposing factors include renal impairment, hepatic impairment, and recent organ transplantation.
Certain types of diuretics are associated with varying levels of risk for ototoxicity. Loop and thiazide diuretics carry this side effect. The loop diuretic furosemide is associated with ototoxicity, particularly when doses exceed 240 mg per hour. The related compound ethacrynic acid has a higher association with ototoxicity, therefore it is preferred only for patients with sulfa allergies. Diuretics are thought to alter the ionic gradient within the stria vascularis  Bumetanide confers a decreased risk of ototoxicity compared to furosemide.
Platinum-containing chemotherapeutic agents, including cisplatin and carboplatin, are associated with cochleotoxicity characterized by high-frequency hearing loss and tinnitus (ringing in the ears). Ototoxicity is less frequently seen with the related compound oxaliplatin. Cisplatin-induced ototoxicity is dose-dependent, typically occurring with doses greater than 60 mg/m2, and tend to occur when chemotherapy is given every two weeks compared to every one week. Cisplatin and related agents are absorbed by the cochlear hair cells and result in ototoxicity through the production of reactive oxygen species. The decreased incidence of oxaliplatin ototoxicity has been attributed to decreased uptake of the drug by cells of the cochlea. Administration of amifostine has been used in attempts to prevent cisplatin-induced ototoxicity, but the American Society of Clinical Oncology recommends against its routine use.
Antiseptics and disinfectants
Topical skin preparations such as chlorhexidine and ethyl alcohol have the potential to be ototoxic should they enter the inner ear through the round window membrane. This potential was first noted after a small percentage of patients undergoing early myringoplasty operations experienced severe sensorineural hearing loss. It was found that in all operations involving this complication the preoperative sterilization was done with chlorhexidine. The ototoxicity of chlorhexidine was further confirmed by studies with animal models.
Several other skin preparations have been shown to be potentially ototoxic in the animal model. These preparations include acetic acid, propylene glycol, quaternary ammonium compounds, and any alcohol-based preparations. However, it is difficult to extrapolate these results to human ototoxicity because the human round window membrane is much thicker than in any animal model.
Ototoxic effects are also seen with quinine, pesticides, solvents, asphyxiants and heavy metals such as mercury and lead. At high doses, aspirin and other salicylates may also cause high-pitch tinnitus and hearing loss in both ears, typically reversible upon discontinuation of the drug. The erectile dysfunction medications Viagra, Levitra, and Cialis have also been reported to cause hearing loss.
When combining multiple ototoxins, the risk of hearing loss becomes greater.
Ototoxic chemicals in the environment (from contaminated air or water) or in the workplace interact with mechanical stresses on the hair cells of the cochlea in different ways. For organic solvents such as toluene, styrene or xylene, the combined exposure with noise increases the risk of hearing loss in a synergistic manner. Carbon monoxide, has been shown to increase the severity of the hearing loss from noise. Given the potential for enhanced risk of hearing loss, exposures and contact with products such as paint thinners, degreasers, white spirits, exhaust, should be kept to a minimum. Noise exposures should be kept below 85 decibels, and the chemical exposures should be below the recommended exposure limits given by agencies such as OSHA, NIOSH, or ACGIH.
Drug exposures mixed with noise potentially lead to increased risk of ototoxic hearing loss. Noise exposure combined with the chemotherapeutic cisplatin puts individuals at increased risk of ototoxic hearing loss. Noise at 85 dB SPL or above added to the amount of hair cell death in the high frequency region of the cochlea In chinchillas. The American Academy of Audiology includes in their position statement that exposure to noise at the same time as ahminoglycosides may exacerbate ototoxicity. The American Academy of Audiology recommends people being treated with ototoxic chemotherapeutics avoid excessive noise levels during treatment and for several months following cessation of treatment.
No specific treatment may be available, but withdrawal of the ototoxic drug may be warranted when the consequences of doing so are less severe than those of the ototoxicity.
It is difficult to distinguish between nerve damage and structural damage due to similarity of the symptoms. Diagnosis of ototoxicity typically results from ruling out all other possible sources of hearing loss and is often the catchall explanation for the symptoms. Treatment options vary depending on the patient and the diagnosis. Some patients experience only temporary symptoms that do not require drastic treatment while others can be treated with medication. Physical therapy may prove useful for regaining balance and walking abilities. Cochlear implants are sometimes an option to restore hearing. Such treatments are typically taken to comfort the patient, not to cure the disease or damage caused by ototoxicity. There is no cure or restoration capability if the damage becomes permanent, although cochlear nerve terminal regeneration has been observed in chickens, which suggests that there may be a way to accomplish this in humans.
Note: Aminoacide can help like Cysteine, Tyrosine
The cochlea is primarily a hearing structure situated in the inner ear. It is the snail-shaped shell containing several nerve endings that makes hearing possible. Ototoxicity typically results when the inner ear is poisoned by medication that damages the cochlea, vestibule, semi-circular canals, or the auditory/ vestibulocochlear nerve. The damaged structure then produces the symptoms the patient presents with. Ototoxicity in the cochlea may cause hearing loss of the high-frequency pitch ranges or complete deafness, or losses at points between. It may present with bilaterally symmetrical symptoms, or asymmetrically, with one ear developing the condition after the other or not at all. The time frames for progress of the disease vary greatly and symptoms of hearing loss may be temporary or permanent.
Two types of otolith organs are housed in the vestibule: the saccule, which points vertically and detects vertical acceleration, and the utricle, which points horizontally and detects horizontal acceleration. The otolith organs together sense the head’s position with respect to gravity when the body is static; then the head’s movement when it tilts; and pitch changes during any linear motion of the head. The saccule and utricle detect different motions, which information the brain receives and integrates to determine where the head is and how and where it is moving.
The vestibule and the semi-circular canals together detect all directions of head movement.
The semi-circular canals are three bony structures filled with fluid. As with the vestibule, the primary purpose of the canals is to detect movement. Each canal is oriented at right angles to the others, enabling detection of movement in any plane. The posterior canal detects rolling motion, or motion about the X axis; the anterior canal detects pitch, or motion about the Y axis; the horizontal canal detects yaw motion, or motion about the Z axis. When a medication is toxic in the vestibule or the semi-circular canals, the patient senses loss of balance or orientation rather than losses in hearing. Symptoms in these organs present as vertigo, difficulties walking in low light and darkness, disequilibrium, oscillopsia among others. Each of these problems is related to balance and the mind is confused with the direction of motion or lack of motion. Both the vestibule and semi-circular canals transmit information to the brain about movement; when these are poisoned, they are unable to function properly which results in miscommunication with the brain.
When the vestibule and/or semi-circular canals are affected by ototoxicity, the eye can also be affected. Nystagmus and oscillopsia are two conditions that overlap the vestibular and ocular systems. These symptoms cause the patient to have difficulties with seeing and processing images. The body subconsciously tries to compensate for the imbalance signals being sent to the brain by trying to obtain visual cues to support the information it is receiving. This results in that dizziness and "woozy" feeling patients use to describe conditions such as oscillopsia and vertigo.
The auditory/vestibulocochlear nerve, or cranial nerve VIII, is the least afflicted component of the ear when ototoxicity arises, but if the nerve is affected, the damage is most often permanent. Cranial nerve VIII "has a vestibular part which functions in balance, equilibrium, and orientation in three-dimensional space, and a cochlear part which functions in hearing." Despite the vestibular or cochlear structures functioning normally, affliction of the nerve effectively arrests communication between these structures and the brain. Symptoms present similar to those resulting from vestibular and cochlear damage, including tinnitus, ringing of the ears, difficultly walking, deafness, and balance and orientation issues.
- Schacht, Jochen; Hawkins, Joseph E. (2006-01-01). "Sketches of otohistory. Part 11: Ototoxicity: drug-induced hearing loss". Audiology & Neuro-Otology. 11 (1): 1–6. doi:10.1159/000088850. ISSN 1420-3030. PMID 16219991.
- American Academy of Audiology (2009). Position Statement and Practice Guidelines on Ototoxicity Monitoring (PDF). AAA.
- Cazals, Y. (2000-12-01). "Auditory sensori-neural alterations induced by salicylate". Progress in Neurobiology. 62 (6): 583–631. doi:10.1016/s0301-0082(00)00027-7. ISSN 0301-0082. PMID 10880852.
- Johnson AC and Morata, TC (2010). "Occupational exposure to chemicals and hearing impairment. The Nordic Expert Group for Criteria Documentation of Health Risks from Chemicals." (PDF). Arbete och Hälsa. 44 (4): 177. Retrieved May 4, 2016.
- Dobie RA, Black FO, Pezsnecker SC, Stallings VL (March 2006). "Hearing loss in patients with vestibulotoxic reactions to gentamicin therapy". Archives of Otolaryngology - Head & Neck Surgery. 132 (3): 253–7. doi:10.1001/archotol.132.3.253. PMID 16549744.
- Basile AS, Huang JM, Xie C, Webster D, Berlin C, Skolnick P (December 1996). "N-methyl-D-aspartate antagonists limit aminoglycoside antibiotic-induced hearing loss". Nature Medicine. 2 (12): 1338–43. doi:10.1038/nm1296-1338. PMID 8946832.
- Wu WJ, Sha SH, Schacht J (2002). "Recent advances in understanding aminoglycoside ototoxicity and its prevention". Audiology and Neuro-Otology. 7 (3): 171–4. doi:10.1159/000058305. PMID 12053140.
- Munckhof WJ, Grayson ML, Turnidge JD (April 1996). "A meta-analysis of studies on the safety and efficacy of aminoglycosides given either once daily or as divided doses". Journal of Antimicrobial Chemotherapy. 37 (4): 645–63. doi:10.1093/jac/37.4.645. PMID 8722531.
- Tepel M (August 2007). "N-Acetylcysteine in the prevention of ototoxicity". Kidney International. 72 (3): 231–2. doi:10.1038/sj.ki.5002299. PMID 17653228.
- Wirmer J, Westhof E (2006). "Molecular contacts between antibiotics and the 30S ribosomal particle". Methods Enzymology. 415: 180–202. doi:10.1016/S0076-6879(06)15012-0. PMID 17116475.
- Esterberg R, et al. (April 2013). "Disruption of intracellular calcium regulation is integral to aminoglycoside-induced hair cell death". Journal of Neuroscience. 33 (17): 4559–12. doi:10.1523/JNEUROSCI.4559-12.2013. PMID 23616556.
- Perez N, Martín E, García-Tapia R (March 2003). "Intratympanic gentamicin for intractable Ménière's disease". The Laryngoscope. 113 (3): 456–64. doi:10.1097/00005537-200303000-00013. PMID 12616197.
- Roland, Peter S. (2004). Ototoxicity. Hamilton, Ont: B.C. Decker. ISBN 1-55009-263-4.
- Voelker JR, Cartwright-Brown D, Anderson S, et al. (October 1987). "Comparison of loop diuretics in patients with chronic renal insufficiency". Kidney International. 32 (4): 572–8. doi:10.1038/ki.1987.246. PMID 3430953.
- Schmitz, PG. Renal:An integrated approach to disease. McGraw Hill, New York NY 2012, pg 123
- Rademaker-Lakhai JM, Crul M, Zuur L, et al. (February 2006). "Relationship between cisplatin administration and the development of ototoxicity". Journal of Clinical Oncology. 24 (6): 918–24. doi:10.1200/JCO.2006.10.077. PMID 16484702.
- Hellberg V, Wallin I, Eriksson S, et al. (January 2009). "Cisplatin and oxaliplatin toxicity: importance of cochlear kinetics as a determinant for ototoxicity". Journal of the National Cancer Institute. 101 (1): 37–47. doi:10.1093/jnci/djn418. PMC . PMID 19116379.
- Rybak LP, Whitworth CA, Mukherjea D, Ramkumar V (April 2007). "Mechanisms of cisplatin-induced ototoxicity and prevention". Hearing Research. 226 (1-2): 157–67. doi:10.1016/j.heares.2006.09.015. PMID 17113254.
- Hensley ML, Hagerty KL, Kewalramani T, et al. (January 2009). "American Society of Clinical Oncology 2008 clinical practice guideline update: use of chemotherapy and radiation therapy protectants". Journal of Clinical Oncology. 27 (1): 127–45. doi:10.1200/JCO.2008.17.2627. PMID 19018081.
- Bicknell, P. G. (1971). "Sensorineural deafness following myringoplasty operations". The Journal of Laryngology & Otology. 85 (09): 957–962. doi:10.1017/S0022215100074272.
- Campo, Pierre; Morata, Thais C.; Hong, OiSaeng. "Chemical exposure and hearing loss". Disease-a-Month. 59 (4): 119–138. doi:10.1016/j.disamonth.2013.01.003. PMC . PMID 23507352.
- Rawool, Vishakha (2012). Hearing Conservation: In Occupational, Recreational, Educational, and Home settings. New York, NY: Thieme. p. 10.
- Fechter L.D. "Promotion of noise-induced hearing loss by chemical contaminants," J. Tox. Env. Health Part A. 67:727-740 (2004)
- Campbell, Kathleen (2007). Pharmacology and Ototoxicity for Audiologists. Clifton Park, NY: Delmar Centrage Learning. p. 145.
- Gratton, Michael Anne; Salvi, Richard J; Kamen, Barton A; Saunders, Samuel S (1990-12-01). "Interaction of cisplatin and noise on the peripheral auditory system". Hearing Research. 50 (1–2): 211–223. doi:10.1016/0378-5955(90)90046-R.
- Laurell, GÖRan; Borg, Erik (1986-01-01). "Cis-Platin Ototoxicity in Previously Noise-Exposed Guinea Pigs". Acta Oto-Laryngologica. 101 (1-2): 66–74. doi:10.3109/00016488609108609. ISSN 0001-6489. PMID 3962651.
- My Deafness. "Ototoxicity: Ear Poisoning". Causes of Deafness and Types of Deafness (Hearing Loss). My Deafness. Retrieved 30 Nov 2011.
- VEDA. "VEDA-VEstibular Disorders Association-Ototoxicity". VEDA-Vestibular Disorders Association. VEDA. Retrieved 30 Nov 2011.
- "Regeneration of Cochlear Efferent Nerve Terminals after Gentamycin Damage". Retrieved 15 November 2014.
- "ototoxicity". The Free Dictionary by Farlex.
- Mudd, Pamela. "Ototoxicity". Medscape Reference. WebMD LLC. Retrieved 30 Nov 2011.
- Farr, Gary. "The Cranial Nerves". Cranial Nerves. BecomeHealthyNow.com. Retrieved 30 Nov 2011.