A type of antibiotics can cause hearing loss - and now we know why

Some life-saving antibiotics can cause hearing loss, and we may now know why. A study in mice suggests it is all down to the effects of inflammation, which is the body’s response to infection. This causes ion channels in the sensory hair cells of the inner ear to become more permeable to the antibiotics – known as aminoglycosides – which then increases the cells’ sensitivity to the drugs’ toxic effects.

Aminoglycoside antibiotics, such as gentamicin, are popular because they work on a broad range of bacteria, unlike most modern narrow-spectrum antibiotics. They are also sometimes used to treat microbes that are resistant to multiple other antibiotics.

“This makes aminoglycosides useful for treating infections where the microbe identity remains unknown,” says Peter Steyger at Creighton University in Nebraska.

Benefits for newborns

As such, the drugs are particularly useful for treating infections in newborns, because these infections can prove fatal within one or two days – too soon for tests to reveal the microbe responsible for the illness.

However, researchers know that aminoglycosides like gentamicin are associated with hearing loss. As a consequence, infants in neonatal intensive care units, where aminoglycosides are used, have rates of hearing loss at least six times higher than among otherwise healthy full-term babies.

To better understand why this class of drugs is linked with hearing loss, Steyger and his colleagues tested the effects of gentamicin on hearing in mice.

They found that infection and inflammation caused the ion channels in sensory hair cells to become more permeable to the drug, leading to more of it being taken up by the sensitive cells in the cochlea of the inner ear. This amplified the toxic effects of the drug on the cells.

Body-wide inflammation

Steyger and his colleagues found that one protein in particular involved in ion channels, TRPV1, facilitated gentamicin’s entry into the hair cells in the presence of inflammation or an immune response. The mice they bred without working TRPV1 were protected from hearing loss caused by gentamicin even in the presence of body-wide inflammation.

In light of these findings, Steyger says doctors should consider using antibiotics that don’t increase the risk of hearing loss in patients with body-wide infection, where possible. But when aminoglycosides are the only option, healthcare professionals can now be on the lookout for those people most likely to need post-treatment auditory rehabilitation much earlier.

“This is especially important in children learning to listen and speak, where delay in identifying hearing loss has lifelong consequences including delayed acquisition of spoken language, less academic success and reduced income,” he says.

Steyger adds that with new techniques that can identify microbes responsible for infection more rapidly, doctors may soon be less reliant on broad-spectrum antibiotics to treat newborns.