Prevention of Noise-induced Hearing Loss

Noise-induced hearing loss (NIHL) affects an estimated 5% of the worldwide population, with 30-40 million Americans exposed to hazardous sound or noise levels regularly. Sources of noise may be occupational (e.g., manufacturing, construction), blast noise (e.g., firearms or explosions), or recreational (e.g., loud music, power tools). Trauma to the inner ear can occur through transient hearing loss (temporary threshold shifts, TTS) or permanent hearing loss (permanent threshold shift, PTS). Although hearing recovers after a TTS in about 24-48 hours, growing evidence suggests that repeated TTS may lead to PTS. Both TTS and PTS lead to a decrease in hearing thresholds at 3000 to 6000 Hz. Currently, there are no treatments for human NIHL although this is an area of active investigation. Protection against NIHL consists of limiting noise exposure through Occupational Safety and Health Administration (OSHA) limits to occupational noise and the wearing of hearing-protection devices (e.g., ear muffs or earplugs). There are no known medications that can be used clinically to prevent NIHL in humans. LePrell and colleagues have successfully established a protocol for inducing TTS using digitally-modified pop or rock music. This model of experimentally-induced TTS was intended to provide an ethical way of testing medications that might prevent NIHL. In a mouse model, Bao and colleagues were able to use zonisamide, an anti-epileptic medication approved for the treatment of partial seizures, and methylprednisolone, a glucocorticoid medication, to protect against noise-induced PTS. The long-term goal of this research is to find medications that can prevent NIHL. The goal of the present pilot study is to evaluate zonisamide and methylprednisolone as medications to prevent TTS in humans. Specific Aim 1: Examine zonisamide as a possible prophylactic medication to prevent noise-induced hearing loss, using an escalating dose protocol. Healthy volunteers would be given 100 or 200 mg of zonisamide as one-time doses or as a daily medication for two week (to establish a steady-state). They would be exposed to digitally-modified pop or rock music for 4 hours and undergo serial testing of hearing and monitoring for side effects after their sound exposure for 3-4 hours. They would be monitored at one day and one week post-exposure for hearing and other side effects. Hypothesis: Zonisamide is able to protect against noise-induced hearing loss in humans. Specific Aim 2: Examine methylprednisolone as a possible prophylactic medication to prevent noise-induced hearing loss, using an escalating dose protocol. Healthy volunteers would be given 32 or 64 mg of methylprednisolone as one-time doses. They would undergo the same music exposure and post-sound exposure monitoring as described above. Hypothesis: Methylprednisolone is able to protect against noise-induced hearing loss in humans