The purpose of this research study is to test the effectiveness and safety of the study drug, AM-111. AM-111 is tested for the treatment of sudden sensorineural hearing loss where the cause is unknown.

This phase III study is assessing the drug's safety and is aiming to demonstrate efficacy of intratympanic AM-111 injections in the treatment of severe to profound idiopathic sudden sensorineural hearing loss (ISSNHL). The active pharmaceutical ingredient of AM-111 is the JNK inhibitor (D-JNKI-1), a synthetic peptide consisting of 31 D-amino acids, which acts as a c-Jun N-terminal kinase (JNK) ligand.

Inclusion Criteria:

1. Unilateral ISSNHL with onset within 72 hours prior to study treatment;
2. Mean hearing threshold of equal to or worse than (≥) 60 dB averaged across the 3 most affected contiguous air conduction audiometric pure tone frequencies ("pure tone average", PTA);*
3. Mean hearing loss of equal to or worse than (≥) 40 dB averaged across the air conducted PTA frequencies compared with the unaffected contralateral ear or reference values from a pre-existing audiogram or ISO 7029;2000 norm values in case of asymmetric hearing prior to the ISSNHL incident;
4. Age ≥ 18 and ≤ 65 years on the day of screening;

Other protocol-defined inclusion criteria may apply.

Exclusion Criteria:

1. Bilateral ISSNHL;
2. Acute hearing loss from noise trauma, barotrauma or head trauma;
3. History of autoimmune hearing loss, radiation-induced hearing loss, endolymphatic hydrops or Menière's disease in the affected ear;
4. History of chronic inflammatory or suppurative ear disease or cholesteatoma in the affected ear;
5. History of acoustic neuroma or other retrocochlear damage in the affected ear;
6. History of otosclerosis in the affected ear;
7. Suspected perilymph fistula or membrane rupture in the affected ear;
8. Congenital hearing loss;
9. History of ISSNHL in the past 2 years;
10. Otitis media or otitis externa that is ongoing or ended within 7 days prior to study treatment;

Other protocol-defined exclusion criteria may apply.