Can antibiotics cause hearing loss?
What if the medication that could save your life could also damage your hearing?
Unfortunately that is a situation faced by patients and their doctors every day. A new study out of Oregon Health & Science University in Portland, Oregon confirmed that a certain class of widely used antibiotics called aminoglycosides causes hearing loss, and researchers are now on a quest to find an alternative.
Aminoglycosides are a class of antibiotics that work by preventing bacterial protein synthesis. What this means is the antibiotic renders the bacterial cells incapable of making proteins, thus weakening the bacteria cells and making them ineffective. Unfortunately, with the super powers of aminoglycosides comes a downside: ototoxicity. An ototoxic medication is one that has the side effect of damage to the cochlea or auditory nerve, and possibly the vestibular (balance) system. Because of the dangerous side effects, which not only include hearing loss but kidney damage as well, the use of aminoglycosides is restricted to life-threatening infections.
Developing hearing loss
In the Portland study, otherwise healthy mice that were given a small amount of an aminoglycoside developed a small degree of hearing loss. However, mice with an inflammation typical of the infections treated with aminoglycosides in humans had a much greater degree of hearing loss when they were given the same antibiotics.
The same effects are seen in humans. "Currently, it's accepted that the price that some patients have to pay for surviving a life-threatening bacterial infection is the loss of their ability to hear," said Peter Steyger, lead author of the study and professor of otolaryngology, head and neck surgery at OHSU. "We must swiftly bring to clinics everywhere effective alternatives for treating life-threatening infections that do not sacrifice patients' ability to hear."
So, how do aminoglycosides cause hearing loss? First off, bacterial infection causes inflammation in the inner ear, among other systems in the body. And when inflammation is present, the amount of aminoglycoside antibiotics that are absorbed by the vulnerable inner parts of the ear increases. When too many of the toxins are absorbed by the inner parts of the ear, specifically the cochlea and auditory nerve, the sensory cells that detect sound and motion are killed.
Understanding the cause
The majority of those who lose their hearing are infants who are given the antibiotics due to a life-threatening infection such as pneumonia, peritonitis or sepsis. Of particular concern are infants in neonatal intensive care units (NICU). Eighty percent of all infants admitted to the NICU receive aminoglycosides; that means each year 480,000 babies have their hearing placed in jeopardy. The rate of hearing loss in babies who have been in the NICU is significantly higher than that of the general infant population, at 2 to 4 percent. To compare, the rate of hearing loss in full-term infants from congenital causes is just 0.1 to 0.3 percent.
Aminoglycosides were developed almost 50 years ago. Though alternatives have been developed, aminoglycosides have an advantage due to the fact that they are not only widely available, but also inexpensive, extremely effective in saving lives and do not require refrigeration.
In the past, hearing loss and aminoglycosides’ ability to fight infection went hand in hand; in other words, eliminating the risk of hearing loss also eliminated the drug’s life-saving potential. As of right now, hearing loss is considered an unavoidable potential side effect to taking these life-saving antibiotics. Anywhere from 20 to 60 percent of adults who are given aminoglycosides experience some degree of hearing loss, from mild to severe.
"The toxicity of these drugs is something we accept as a necessary evil,” said Daria Mochly-Rosen, Ph.D., director of SPARK, a program at Stanford that provides funding and support to get new medications from the lab into action.
Coming up with a plan
Fortunately, thanks to researchers at Stanford, there may be an alternative on the horizon. The hope is that a new form of aminoglycoside currently under development at the Stanford School of Medicine will have the same life-saving properties without the resulting hearing loss. In a recent study, a modified form of aminoglycoside known as N1MS was able to successfully cure infections in mice without causing hearing loss.
Instead of attempting to protect vulnerable structures in the inner ear by removing the infection-fighting properties which caused the damage, the scientists tried a different approach. The result was N1MS, which blocks the drug's access to the sensory hair cells completely. In trials, researchers were successfully able to cure mice of infections without the resulting hearing loss that typically accompanies the use of aminoglycosides.
Next up for N1MS is human testing, and researchers are optimistic. “If we can eventually prevent people from going deaf from taking these antibiotics, in my mind, we will have been successful,” said Anthony Ricci, Ph.D., professor of otolaryngology-head and neck surgery and co-senior author of the Stanford study. “Our goal is to replace the existing aminoglycosides with ones that aren’t toxic.