Intranasal drug delivery has been recognized as a non-invasive and efficient route for targeting the central nervous system (CNS) and has received considerable attention. The blood–brain barrier (BBB) is one of the main challenges in neurotherapeutics as it limits the access of most pharmacological agents to the brain. The intranasal route offers a unique alternative for the direct transport of drugs through the olfactory and trigeminal pathways, circumventing the BBB. This review discusses the structural and physiological features of the nasal cavity that favor drug absorption and the mechanisms of nose-to-brain transport, including intracellular and extracellular pathways. Apart from the fundamentals, this article covers various intranasal formulations such as liquid sprays, semisolids (gels, ointments) and solid systems (microparticles, nanoparticles) and the role of bioadhesive polymers, penetration enhancers, solubilizers and antioxidants in improving the drug stability and absorption. Special emphasis is placed on the therapeutic potential of intranasal delivery in neurological and neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, epilepsy, and migraine, where traditional drug administration often fails to achieve effective concentrations in the brain. Although mucociliary clearance, enzymatic degradation and inter-individual variability present challenges, advances in nanotechnology, polymer science and device development are helping to overcome these limitations.
Kaushik et al. (Fri,) studied this question.