Both drugs used are already known to protect hearing on their own, but this study, performed by researchers at Washington University School of Medicine in St. Louis, has been the first to test the two in combination.
"We found they have synergy," says Jianxin Bao, PhD, research associate professor of otolaryngology at the School of Medicine, and continues: "Two drugs at lower dosages can block more signaling pathways than one alone, improving results while reducing side effects.”
From earlier studies the researchers have concluded that anticonvulsant drugs for treating epilepsy helped protect hearing in mice after exposure to loud noise. Other researchers had determined that glucocorticoids, anti-inflammatory drugs often used to treat allergies and asthma, were also protective.
For this study, Jianxin Bao and colleagues chose two drugs from the anti-epilepsy family and two from the glucocorticoid family.
To test each drug's ability to prevent hearing loss, the researchers gave various doses to mice two hours before exposing them to noise. To test the drug's ability to treat hearing loss, they gave the drugs to different groups of mice 24 hours after noise exposure.
Three of the four drugs showed increasing protection with higher doses, while two of the drugs in combination, the anticonvulsant zonisamide and the glucocorticoid methylprednisolone, showed comparable hearing protection at much lower doses than when administered alone.
Cocktail reduces hearing loss
While the drugs do not prevent all hearing loss following ongoing exposure to noise at 110 decibels, they can significantly reduce the loss by about 10 to 30 decibels. In other words, a mouse with normal hearing might be able to hear a sound at 30 decibels, but after exposure to loud noise, that mouse might only hear sounds that reach 50 decibels. If that mouse were treated, it might be able to hear sounds at 40 decibels. In humans, protecting 5 or 10 decibels makes a difference in being able to hear everyday speech.
Jianxin Bao says that the next step is to test the drugs in animals that model human hearing more closely.
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