Formulation considerations in enhancing olfactory mucosal deposition for nose-to-brain drug delivery

Nose-to-brain (N2B) drug delivery offers a promising alternative to circumvent the blood-brain barrier and deliver therapeutic agents directly to the central nervous system. Among the intranasal pathways, targeting the olfactory mucosa is particularly attractive due to its direct anatomical and functional connection to the brain. However, effective deposition and retention of drug-loaded formulations in the olfactory region remain significant challenges, owing to complex nasal anatomy, mucociliary clearance, and limited surface area. This review critically examines the physiological and anatomical barriers to olfactory targeting and highlights recent advances in nanoparticle-based strategies designed to enhance mucosal deposition and transport. Various formulation approaches-including mucoadhesive polymers, surface-functionalized nanocarriers, and stimuli-responsive systems-are discussed alongside innovative delivery devices and administration techniques tailored for olfactory mucosal delivery. In vitro, ex vivo, and in vivo models used to evaluate these strategies are reviewed, as are safety, regulatory, and translational considerations. Finally, the review explores emerging technologies such as patient-specific delivery platforms and smart nanoparticles, offering a forward-looking perspective on the future of N2B therapeutics for neurological disorders.