Nose-to-brain drug delivery: Challenges and progress towards brain targeting in the treatment of neurological disorders

Delivery of therapeutics to the central nervous system for treating psychiatric and neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease, is a rigorous task due to the presence of blood-brain barrier (BBB) and cerebro-spinal fluid barrier. To overcome the limitations caused by these barriers, different novel drug delivery systems have been developed. Intranasal drug delivery has gained emerging interest as the nasal cavity is in close proximity to the brain. It also contains nerves, which provide direct delivery of drugs to the brain. It is a non-invasive method with no first-pass metabolism, high absorption, high permeability, and better patient compliance. This review provides a better understanding of formulation approaches used for brain delivery, factors affecting brain drug delivery, the mechanism responsible for nose-to-brain delivery, and strategies used to overcome various physiological barriers.