Microemulsion as a promising carrier for nose to brain delivery: journey since last decade

Abstract

Tight junctions and efflux transporters are two chief bodyguards of the blood–brain barrier that protect the brain and create challenges for the treatment of neurological disorders by hampering the systemic delivery of conventional therapeutics to the brain. Approaches involving drug delivery across the brain are either invasive which require disruption of barrier integrity, leading to develop the risk of neurological changes and brain abscess, or non-invasive patient friendly approach like intranasal delivery. Several investigations have strongly confirmed the direct connection between nose and brain via olfactory and trigeminal pathway which deliver neurotherapeutics directly to the brain bypassing obstructive barriers. Since last two decades, extensive researches are ongoing for intranasal delivery of drugs in the form of different novel colloidal carriers wherein, microemulsion with their unique composition and small globule size (< 100 nm) have shown higher efficacy in-vivo and revealed their great potential to treat severe brain disorders where rapid onset of action is needed. In this discussion, why intranasal delivery of microemulsion seems to be promising for brain targeting is the foremost focus while, the importance of delivery device for efficient brain targeting is also covered. Considering the translation of positive in-vivo outcomes further into clinical studies and humans, future direction should be aimed at evaluating the suitability of microemulsion with an efficient intranasal delivery device capable of delivering formulation into upper nasal segment. Limitations associated to intranasal delivery of microemulsion such as performing brain distribution studies in most appropriate model resembling humans, impact of diseased condition on the drug absorption and toxicity related to prolonged use, etc. must be addressed in the near future to establish a strong bench to bedside platform.