Intratympanic drug delivery systems to treat inner ear impairments

Background Sensorineural hearing loss (SNHL) is a disorder that significantly affects human quality of life. Current treatment for SNHL is still limited to hearing aids and cochlear implants. A better understanding of the etiological mechanisms of SNHL will facilitate the elucidation of the oto-protective efficacy of various novel therapeutic molecules. Intratympanic (IT) administration appears to be an attractive route for the delivery of these agents into the inner ear due to its advantages over systemic and cochlear administration. However, this administration route is limited by Eustachian tube clearance, transport capacity through the round window membrane (RWM), and the intrinsic structure of the cochlea, leading to the necessity of developing advanced drug delivery systems to improve the efficacy of IT administration. Area covered In this review, we summarize and discuss various drug delivery systems applied to IT administration, including conventional formulations and combinations of hydrogels and nanoparticles such as polymers, lipids, inorganic, and hybrid nanoparticles. Expert opinion A variety of innovative injectable systems have been prepared, and they have been demonstrated in several research models to have a significantly better ability to deliver drugs to the inner ear than that of conventional dosage forms. Hydrogels take advantage of prolonged residence time in the middle ear, while nanoparticles can enhance drug stability and cellular uptake, and allow drug targeting to specific cells. The combination of these two strategies is a promising area for future investigation.