FX-322 in Adults With Stable Sensorineural Hearing Loss

Inclusion Criteria: 1. Adults aged 18-65 years inclusive. 2. Established diagnosis of stable sensorineural hearing loss by standard audiometric measures for ≥ 6 months prior to the Screening visit (no changes in air conduction greater than 10 dB at a single frequency or greater than 5 dB at two contiguous frequencies from the prior audiogram to the Screening audiogram in the study ear). 3. Documented medical history consistent with hearing loss being caused by noise exposure or sudden sensorineural hearing loss. 4. Pure Tone Audiometry (PTA) within 26-70 dB in the ear to be injected. 5. Female subjects must be of non-childbearing potential or will need to utilize two methods of highly effective contraception during the study participation (e.g. hormonal contraception or an intrauterine device and condoms) or remain abstinent. Male subjects should use condoms with spermicide during the course of the study or remain abstinent. Subjects should not donate sperm or ova during the study period. Exclusion Criteria: 1. Previous participation in FX-322 clinical trial. 2. Currently on any medication consisting of valproic acid, valproate sodium, or divalproex sodium. 3. Perforation of tympanic membrane or other tympanic membrane disorders that would interfere with the delivery and safety assessment of an intratympanic medication or reasonably be suspected to affect tympanic membrane healing after injection in study ear. This includes a current tympanostomy tube. 4. Any conductive hearing loss of greater than 15 dB at a single frequency or greater than 10 dB at two or more contiguous octave frequencies in the study ear at the Screening visit or on the prior audiogram (if the Investigator feels there is not a true conductive hearing loss, the Medical Monitor should be consulted). 5. Active chronic middle ear disease or a history of major middle ear surgery, as an adult, in the ear to be injected. 6. Subject has had an intratympanic injection in either ear within 6 months of the screening visit. 7. History of clinically significant vestibular symptoms at the discretion of the investigator. 8. History of clinically significant systemic autoimmune disease. 9. History of head or neck radiation treatment or exposure. 10. History of platinum-based chemotherapy treatment. 11. Exposure to another investigational drug within 28 days prior to injection of study drug. 12. Evidence of any active or chronic disease or condition that could interfere with, or for which the treatment of might interfere with, the conduct of the study, or that would pose an unacceptable risk to the subject in the opinion of the investigator following a detailed medical history, physical examination, and vital signs (systolic and diastolic blood pressure, pulse rate, body temperature). 13. History of substance abuse within 2 years of the Screening Visit. 14. Positive test for drugs of abuse at screening. 15. Positive urine pregnancy test or breast-feeding. 16. Any known factor, condition or disease that, in the view of the Investigator, might interfere with treatment compliance, study conduct or interpretation of the results (e.g. previous high-dose aminoglycoside treatment).