Efficacy of SENS 401 in Subjects With Severe or Profound Sudden Sensorineural Hearing Loss

The main criteria for inclusion: * Male or female aged at least 18 years old * Patients with unilateral idiopathic sudden sensorineural hearing loss or unilateral/bilateral acute acoustic trauma leading to sudden sensorineural hearing loss. * Patients with sudden hearing loss with onset within 96 hours prior to prior to first study drug intake. * Patients under highly effective contraception The main criteria for exclusion: * Bilateral idiopathic hearing loss * Fluctuating hearing loss * History of asymmetric hearing (\>20 dB difference between ears) to the best knowledge of the patient * Severe hearing loss (\>90 dB) associated with unilateral (ipsilateral) complete vestibular loss. * History of Ménière's disease, autoimmune hearing loss, radiation-induced hearing loss, acoustic neuroma (schwannoma), otosclerosis, suspected perilymph fistula or membrane rupture, suspected retro-cochlear lesion, or barotrauma * Previous SSNHL in the affected ear within the past 6 weeks * Complete loss of peripheral vestibular function on the affected side * Any drug-based therapy for inner ear hearing loss that is ongoing or was performed in the past 6 weeks (except oral corticosteroids) * Any ongoing or planned concomitant medication for the treatment of tinnitus until 6 weeks after administration. * Any therapy known as ototoxic (e.g. aminoglycosides, cisplatin, loop diuretics, quinine etc.) at the current time or in the past 6 months or planned in the coming 3 months. * Acute or chronic otitis media or otitis externa terminated less than 7 days * Prior ear surgery of any kind (except ventilating tubes), or cochlear implants * Known history of, or concomitant severe hepatic, gastrointestinal, cardiovascular, respiratory, neurological (except vertigo or tinnitus), hematological, renal, dermatological or psychiatric disease or substance abuse * Neurological disorders including stroke, demyelinating disease, brain stem or cerebellar dysfunction within the last 3 months. * Treatment with any investigational agent within 4 weeks or any past treatment with azasetron or with 5-HT3 antagonists, or any prior or planned treatment by antidepressant treatment containing serotoninergic agents. * Patients with either a history of significant arrhythmia, or a history of conditions known to increase the proarrhythmic risk (e.g., congestive heart failure, long QT Syndrome, hypokalemia etc...).