Drug Side Effects on Audiological and Vestibular Testing

There are over 2,000 drugs and more than 400 side effects that could impact the accuracy of the audiometric or vestibular evaluation and the recommendations made for intervention and management (DiSogra, 2008, 2001). 

During clinical trials, incidence figures of an adverse event (side effect) might be extremely low and reported as “rare” or “less frequent.” One person in 100 might report that their ears are ringing, however it could be reported as tinnitus, roaring, ear disturbances, or auditory hallucinations.

There is a wealth of drug information available on the internet, but it is incumbent on you to know what websites provide reliable, accurate, and up-to-date information especially reported adverse reactions or side effects.

Some websites that offer reliable drug information include (but not limited to): www.drugs.com, www.rxlist.com, www.earserv.com.drugs (audiology-specific side effects), and www.epocrates.com. The aforementioned websites do not represent an endorsement by the author or the American Academy of Audiology. 

Audiology 101—The Case History

Typical case history questions to the patient are: “What medications are you currently taking?” “Why are you taking them?” “How long have you been taking them?” As simple as these questions are, it is the first step for possible problems.

A survey in the United States of a representative sampling of 2,206 community-dwelling adults (aged 62–85 years) was conducted by in-home interviews and use of medication logs between 2010 and 2011. At least one prescription medication was used by 87 percent of those surveyed. Five or more prescription medications were used by 36 percent, and 38 percent used over-the-counter medications (Qato, 2016). The Centers for Disease Control and Prevention (2016) estimated 75 percent of persons older than age 60 take two or more drugs, and those older than 90 take five or more medications.

In addition to pharmaceuticals, Kennedy (2005) reported that an estimated 38.2 million adults in the United States used herbs and/or supplements in 2002. Of interest is that only a third of the participants told their health-care provider about their herb or supplement use.

Medication side effects may influence an older patient’s understanding of your question(s) or test instructions and capacity to stay focused on the required task for a particular test. For example, some medications might have an obvious auditory side effect (e.g., tinnitus), might influence vestibular testing (e.g., oculomotor dysfunction), or have a cognitive side effect (e.g., confusion).

According to Rochon (2016), the possibility of an adverse drug event (ADE) should always be borne in mind when evaluating an older adult; any new symptom should be considered drug–related until proven otherwise. Pharmacokinetic changes lead to increased plasma drug concentrations and pharmacodynamics changes lead to increased drug sensitivity in older adults. 

Clinicians must also be alert to the use of herbal and dietary supplements by older patients, who may not volunteer this information and are prone to drug–drug interactions related to these supplements. 

For drug–drug interaction information, click here. For drug–herbal interactions, click here.

Timelines: Pharmacist/Audiologist Relationship

Whether you are conducting an audiometric evaluation, a vestibular study, or a tinnitus evaluation, establishing a timeline from when the symptoms first began and when the drug was started should be the focus of your case history and differential diagnosis. 

Even if you believe that the patient is a good historian, memory impairment can be a drug side effect. A patient might report that he or she has been taking a particular drug for about a year. A phone call to the referring physician or pharmacist will help you get the start date (the patient might have been taking it for three years!). For over-the-counter products, the store receipt is the only way to know—if the receipt is even kept.

Audiogram Accuracy: Pure Tones and Speech

So how do we really know that a pure-tone threshold is truly threshold for an older patient? We don’t. For example, your 80-year old patient presents with a flat 70dB sensorineural loss with some high-frequency roll-off. But during the case history, she is not raising her voice or leaning in with behavior consistent with significant hearing loss. She is sitting four to five feet from you and is answering your questions appropriately even when your mouth is not visible to her.

Is that 70dB loss real? Or is it a 35–40dB loss influenced by poor listening skills or an inability to stay focused on the task because of an adverse drug reaction?

Another dilemma is when masking is introduced into the test protocol. Two competing stimuli might be an acoustic overload for an older patient. Are those air-bone gaps real? 

We also rely on word recognition scores for many reasons, especially hearing aid candidacy. Therefore, we must recognize that there are many drugs that have cognitive side effects (See TABLE 2). The possibility exists that these medications might be influencing the test scores. Fatigue influences concentration. You may need to use a shorter word list. Subsequently, data can be misinterpreted as a “change”—but it might not be a true change. 

Middle-Ear Side Effects

Aside from hearing loss and tinnitus, there are several drug effects that can affect the middle ear (congestion/pressure) or the facial nerve. Acoustic impedance and middle-ear muscle relfex testing can identify the presence of pathology.

Vestibular Side Effects

Fifty-five percent of the side effects listed in Appendix I and a third of the herbal medicine side effects in Appendix II can influence a vestibular study. Therefore, you need to explore the possibility that the patient’s current drug regimen might be the cause of their problem or influence your data and subsequent interpretation and recommendations. Establishing the time lines becomes very important. 

In a personal interview (2016) with Dr. Richard Gans, Director of the American Institute of Balance, and an authority on balance testing, he noted that [when looking at a patient’s eye movements] saccadic pursuit, bilateral, bithermal caloric weaknesses or reduced gain using rotary chair is never a unilateral event. The conjugate movements of the eyes during active head rotation is never drug related. Dr. Gans also recommends a thorough review of the patient’s current drug and herbal medicine regimen and establishing symptom/drug time lines as a critical component of the case history.

Cognitive Side Effects

• Is your patient really a poor test taker? 
• Or not cooperating? 
• Are you suspecting malingering? 
• What recommendations will be inappropriate if their drug side effects are not examined? 

Humes (1996) reported that threshold elevation could account for nearly all of the changes in speech perception with age (in quiet or in less demanding listening environments).

Sweetow (2013) reported that the speed of word recognition is reduced with age, as is the patient’s working memory. There are also attention difficulties as well as a decrease in sentence identification because of changes in working memory.

Personal experience has shown that you may want to consider deducting 5-10dB from the reported threshold for elderly patients to compensate for the possibility, if not probability, that the audiogram is not accurate because of cognitive decline (i.e., poor listening). Over-fitting with hearing aids could occur if you take the audiogram at face value. 

Confusion, as a side effect, can be exacerbated when masking is used during air or bone conduction testing as well as speech audiometry. If there is a decrease in the word recognition score, how sure are you that it is not from a drug side effect?

TABLE 3 shows the reported cognitive side effects of prescription medications (Kennedy, 2009) and herbal medications (Handler, 2008). 

Confusing a Drug’s Name—Zocor^® or Zoloft^®?

It is not unusual for patients to confuse the names of the medications they take. For a complete list of sound-alike drug names that can be printed out for reference here.

Dementia Patients 

According to the Alzheimer’s Organization an estimated 5.4 million Americans of all ages have Alzheimer’s disease in 2016. Of the 5.4 million Americans with Alzheimer’s, an estimated 5.2 million people are age 65 and older, and approximately 200,000 individuals are younger than age 65 (younger-onset Alzheimer’s). One in nine people age 65 and older has Alzheimer’s disease. By 2050, the number of people age 65 and older with Alzheimer’s disease may nearly triple, from 5.2 million to a projected 13.8 million, barring the development of medical breakthroughs to prevent or cure the disease.

According to the National Institutes on Deafness and Other Communication Disorders (2016), approximately one in three people in the United States between the ages of 65 and 74 have hearing loss, and nearly half of those older than 75 have difficulty hearing. Factor in the diagnosis of dementia, and more challenges face the audiologist in the evaluation process of a geriatric patient with this diagnosis. The primary caregiver now becomes your historian. Contacting the primary care physician or pharmacist will help with drug names and timelines if the caregiver is not able to provide you with the answers to the patient’s drug history.

Tinnitus Side Effects

More than 220 drugs listed in the Physician’s Desk Reference have tinnitus as a reported side effect (Kennedy, 2009). When did the symptom start? Was there a drug introduced or a dosage increase at the same time? 

Vascular Side Effects

Auditory symptoms of such as fluctuating hearing levels and throbbing tinnitus strongly suggest a vascular problem. TABLE 4 shows the reported vascular side effects of prescription drugs (Kennedy, 2009) and herbal medications (Handler, 2008).

Neurological Side Effects

Medication side effects can also affect the brain, the spine, and the peripheral nerves, some of which could have an impact on our data collection and/or interpretation and recommendations. TABLE 5 shows the reported neurological side effects of prescription drugs (Kennedy, 2009) and herbal medications (Handler, 2008).

Speech Side Effects

Because our patient interaction requires our patients to give verbal responses (i.e. word recognition tests), consider the speech-related side effects of prescription drugs (Kennedy, 2009) and herbal medications (Handler, 2008) that appear in TABLE 6. Assuming that the examiner has normal or near-normal hearing, an expressive speech side effect might have the audiologist interpret the response as an incorrectly spoken word.

Wrong Diagnosis Equals Wrong Intervention

Confidence levels must be very high when making recommendations for medical or surgical intervention or hearing aid intervention. Some questions to ask include the following:

• Do the test results support the patient’s complaint(s)?
• Is the loss truly sensorineural, conductive or mixed? 
• Are the abnormal eye movements truly peripheral or central in origin?

Look back at those patients who could not adjust to amplification. How well did we counsel them? Was it them or did you miss “something?” Did you interpret the audiogram at face value?

That something might be the accuracy of their test that might have been influenced by an adverse drug reaction in addition to their cognitive abilities.

Reporting Your Findings and Suspicions 

Document everything and report your concerns about patient alertness, test accuracy, or other different or unusual observations before, during, and after the testing. Record the time of day that the testing occurred because some medications need to be taken at specific times. Report your discovery of any drug timelines. Note any observations of behaviors during the testing that you believe might have influenced the test results. If it’s not documented, it didn’t happen.

Contacting the Drug’s Manufacturer

All drug manufacturers are required to collect post-Food and Drug Administration (FDA) approval for a period of 10 years. Side effects might emerge after FDA approval that might require a change in drug information in the literature.

Using the “Contact Us” tab on the manufacturer’s website is the easiest way to express your concerns. 

Sample email: “My name is ________________ and I am audiologist. One of my patients, a healthy 50-year old female, began taking ________________ exactly three weeks ago. She is now reporting tinnitus in both ears. The tinnitus started the first day she started the medication. I noted in your literature about this drug that tinnitus, or any other ear-related adverse event, was not reported during clinical trials. Do you have any post-FDA approval information about tinnitus as a new side effect?”

This type of inquiry will be answered within 24 to 48 hours by a pharmacologist who is a product specialist. He or she may have some additional information for you or send you paperwork to complete to report this new adverse event to the FDAs safety information and adverse event reporting program—MedWatch. There is also a section on reporting adverse events with dietary supplements.

Another reporting agency is the Institute for Safe Medical Practices. The same information can be reported for follow-up.

Conclusion

No one is knowledgeable of all of the FDA-approved drugs and their side effects; however, there are reliable (and valuable) websites available that provide accurate and up-to-date information about side effects. Contacting a drug’s manufacturer is simple and you might find some additional information that could be helpful to you and your patient. If in doubt, call the patient’s pharmacist. Incidence figures for some side effects can be very small but they must be considered when there are test discrepancies. Documentation of behaviors is very important. Discovery of and drug-symptom timelines might explain test discrepancies.

Suggestions to reduce the possibility of drug influences on audiological/vestibular testing include the following: 

1. Spend more time in getting an accurate case history. If the patient cannot recall the name(s) of the drug(s) he or she is taking, call his or her pharmacist.
2. Reference www.rxlist.com, www.drugs.com, www.earserv.com/drugs or epocrates.com for side effects. Note: These websites are not an endorsement by the author or the American Academy of Audiology.
3. Establish “time lines” from when the problem began and when the drug(s) were prescribed (see #1). 
4. Make certain that your patient understands the test instructions.
5. Never forget what you learned in Audiology 101 about test/retest reliability. 

Disclaimer

The views and opinions expressed in this article are those of the author and do not necessarily represent the official policy, position, or opinion of the American Academy of Audiology; further, the Academy does not endorse any products or services mentioned in this article.