Researchers at Washington University School of Medicine have found that the antibiotic Kanamycin (KM), which was previously believed to damage ears, actually has a protective effect against hearing loss in young mice when used in low doses.

KM is an antibiotic used to isolate bacteria and treat a variety of infections. It can also lead to severe hearing loss in both human and animals, however.

“Previous animal studies have shown that, when animals are given Kanamycin antibiotic and then exposed to noise, the animals will be more susceptible to noise,” said William Clark, professor of otolaryngology and director of the Program in Audiology and Communication Sciences, a division of the Central Insitute for the Deaf School at Washington University School of Medicine. “Therefore, we fully expected that the antibiotic would make young mice’s ears more susceptible to noise. Instead, we found that the drug completely protected the mouse from any hearing loss.”

The incident that gave rise to the study was a concern raised by an air nurse when she was supervising the transport of newborn babies from remote regions to St. Louis Children’s Hospital by helicopter. She was worried about the potential harm to infants’ hearing caused by exposure to loud noise from the helicopter. She expressed her concern to Clark, who approached the problem from a different perspective. Clark was concerned about the damaging effect of the antibiotic that was given to those premature babies to prevent against infections.

“From the laboratory we know that giving these drugs might in fact make the babies lose more hearing,” Clark said. “I thought maybe doctors should not give those infants the antibiotics because the risk of hearing loss outweighs the benefits of protecting against the infections.”

Due to the vulnerability of these babies, it was not possible to test on them directly. Clark and his colleagues turned to a laboratory study on young mice to see the effect of the drug-noise interaction.

“This particular kind of mouse has been used in lots of studies of effects of noise on hearing,” said Elizabeth Fernandez, a doctoral student in the Program in Audiology and Communication Sciences, who graduated last year from the School of Medicine. “It is a well-established model for human hearing.”

The results appeared to be the opposite of what was originally expected. Mice treated with low-dose KM prior to the exposure of noise were completely protected from sensory cell loss. Extended intervals between KM treatment and noise exposure also demonstrated that the protective effect of the drug-noise interaction could last for up to 48 hours.

“This is the first time that we see any protective effect has been demonstrated by a drug that causes hearing loss against noise that also produces damage to ears,” Clark said. “I thought that the doctor was making a mistake by giving [the] antibiotic to the babies being put on the helicopter. It turns out that it became exactly the right thing to do.”

Researchers have considered the possibility of KM as a method of preconditioning. Medical preconditioning refers to initiating a mildly injurious event in a way that serves to prevent against a later, more injurious event. In this case, low-does KM may have initially led to some minor sensory cell loss, thus providing subsequent protection against severe damages.

“The study has now been focused on identifying critical genes and pathways that this protective effect involves,” Fernandez said. “There could be a specific gene that protects the young mice from the damage. If we could discover the mechanisms that this protective effect uses, we might be able to create a medication that can either prevent the hearing loss or increase the resistance to hearing loss.”