Drug combo helps protect hearing
By ANIThursday, February 24, 2011
WASHINGTON - Scientists at Washington University School of Medicine in St. Louis have identified a low-dose, two-drug cocktail that reduces hearing loss in mice when given before they are exposed to loud noise.
The drugs, already FDA-approved for other conditions, also treat hearing loss after noise exposure.
While both drugs are known to protect hearing on their own, this is the first study to test the two in combination.
“We found they have synergy,” said Jianxin Bao, research associate professor of otolaryngology at the School of Medicine.
“Two drugs at lower dosages can block more signaling pathways than one alone, improving results while reducing side effects. We got the idea from cancer and HIV studies that use multiple drugs at lower dosages,” he said.
Bao’s group have previously found that anticonvulsant drugs for treating epilepsy helped protect hearing in mice after exposure to loud noise. And other groups had determined that glucocorticoids, anti-inflammatory drugs often used to treat allergies and asthma, were also protective.
The reasons these drugs reduce noise-induced hearing loss are not well understood. But anticonvulsants are known to block calcium channels in nerve cells, and Bao’s group speculates that the drug helps protect neuronal connections between hair cells and auditory neurons.
In the study, Bao’s team chose two drugs from the anti-epilepsy family and two from the glucocorticoid family.
To test each drug’s ability to prevent hearing loss, they gave various doses to mice two hours before exposing them to noise. To test treatment, they administered the drugs to different groups of mice 24 hours after noise exposure.
3 of the 4 drugs showed increasing protection with higher doses. And 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.
While the drugs do not prevent all hearing loss following sustained exposure to noise at 110 decibels, or about the sound of a chain saw, they can significantly reduce the loss by about 10 to 30 decibels.
The study was presented Feb. 21 in Baltimore at a meeting of the Association for Research in Otolaryngology. (ANI)
