In otosclerosis, one of the tiny bones of the middle ear is unable to move normally. Sounds cannot be transferred to the inner ear and a conductive hearing loss ensues. The disorder is usually treated by an operation where the bone is replaced by a prosthesis. This restores hearing at low sound frequencies. At high frequencies, surgery is less effective. The smaller effect at high frequencies is probably caused by surgically induced inner ear damage.

Animal studies have shown that the drug acetylcysteine can protect the inner ear against damage. It is not known whether the drug has similar effects in humans. This study will assess the efficacy of acetylcysteine in patients undergoing surgery for otosclerosis.

Inclusion Criteria:

• Otosclerosis where surgery is planned
• Air / bone gap larger than 20 dB
• Normal middle ear status

Exclusion Criteria:

• Hypersensitivity to acetylcysteine
• Deafness on the other ear
• Stapedotomy previously performed on the ear
• Pregnancy
• Asthma