Inner ear drug delivery: Recent advances, challenges, and perspective.

Effective and safe treatment of auditory and vestibular diseases has become increasingly dependent on inner ear drug delivery systems. This review highlights recent advances in inner ear drug delivery research and technologies. The focus is on strategies to overcome delivery barriers and to improve drug residence and targeting, with special attention to in vivo animal and human studies. The research in gene and stem cell delivery to the inner ear is briefly reviewed. Newly developed research tools to address experimental challenges and safety issues are discussed. Local drug delivery to the inner ear with non-invasive or minimally invasive approaches still remains challenging. Nanocarrier-based systems with sustained and targeted delivery properties may be promising for future clinical applications. Precisely controlled intratympanic and intracochlear administration with minimized trauma to the delicate inner ear represents the future perspective in inner ear drug research and development. Trans-oval window delivery may be promising as it allows direct delivery of drugs to the vestibule for vestibular disorders while avoiding the undesired effects due to drug distribution to the cochlea.