The treatment recommended to James for dealing with his lung cancer is a combination of radiation and chemotherapy using the platinum agent cisplatin in combination with a non-platinum chemo agent. Here’s the dilemma: James already has a hearing loss and cisplatin may cause further loss. In the end he chooses a better chance for survival with no hesitation. Still, when the first dose of cisplatin causes a large drop in hearing, he asks if there isn’t something that can be done. James receives steroid injections through the eardrum, quick and nearly painless, which bring back the hearing to its former levels. Next comes a trial of similar injections just prior to each dose of chemo, to prevent further hearing loss.
Prescription medications can harm the inner ear, causing deafness, tinnitus, and imbalance. The term ototoxic comes from oto = ear plus toxin = poison. Ototoxic drugs are usually used to treat life-threatening cancer or infection and on occasion to treat high blood pressure, kidney failure, or severe arthritis. Kidney failure itself can cause high levels of drugs that are excreted through the kidneys, increasing ototoxicity. Some ototoxic drugs, such as aspirin and quinine in high dosage, cause only temporary hearing loss and tinnitus.
Toxicity occurs when medications damage the hair cells of hearing or balance. These sensory cells are among the most fragile in the body. Up to half of all people receiving cisplatin may lose hearing. And about 3 percent of people taking aminoglycoside antibiotics (gentamicin, streptomycin, tobramycin, kanamycin, and amikacin) will also experience ototoxicity.
Genetics and Ototoxicity
A genetic abnormality that causes high sensitivity to aminoglycoside antibiotics occurs in about one in a thousand newborns. Nearly all people with this genetic defect lose hearing after exposure to aminoglycosides. Research is underway to determine if routine screening for this gene should be performed in people about to take aminoglycosides. The genetic disorder is passed on only by the mother. Unfortunately, in many cases there is no adequate alternative to replace this powerful class of antibiotics.
Symptoms of Ototoxicity
When medications damage the hair cells of the cochlea, the symptoms are hearing loss and tinnitus. Many people become aware of the tinnitus first. Damage to the hair cells of the balance system results in dizziness, imbalance, and vertigo.
Medications That Are Ototoxic
Ototoxic drugs can be categorized by the type of drug and whether the effects are permanent or temporary (table 24.1).
What can be done? Precautions are taken when it becomes necessary to prescribe an ototoxic drug. First, you should be informed about high risks and requested to give your consent to treatment. Second, you should have a hearing test before treatment and have your hearing monitored throughout the treatment. Third, drug levels should be monitored in the case of ototoxic antibiotics to make sure you are receiving the right amount. This is especially true in the case of kidney or liver failure, which may raise drug concentrations to toxic levels.
Monitoring consists of testing the hearing periodically during and after a course of chemotherapy. In addition to the usual audiogram that tests the frequencies 250 Hz to 8,000 Hz, audiograms should be done to test the ultra-high frequencies from 8,000 Hz to 12,000 Hz, as these frequencies are the first to show hearing loss. Evidence of hearing loss should trigger an immediate consultation with an ear specialist.
Table 24.1
Ototoxic Medications and Their Effects on Hearing
It is thought that increasing hydration and slowing administration of anti-cancer agents results in less inner ear damage. These two modifications in protocol are associated with lower chemo levels in the blood but longer periods of exposure. Hearing may be preserved and slower administration does not seem to reduce success in treating cancer.
Preliminary research has shown that steroids can reduce ototoxicity of some chemotherapy agents. In addition, combination of platinum-agent and non-platinum chemotherapy for lung cancer may allow a lower dose of platinum and reduce ototoxicity. Antioxidants may be effective in reducing hearing and balance loss from aminoglycoside antibiotics.