Nasal cavity transport routes

As discussed above, nasal sprays tend to deposit at their impaction site, in the anterior, unciliated regions of the nasal cavity, where airflow associated with inspiration is high and mucociliary clearance is slow or erratic. Thus a drag moiety depositing in this region is cleared slowly and is transported over a large area en route to the pharynx. These factors promote drag absorption. 

Small molecules such as cocaine and cephalexin can be transported directly to the CNS from the nasal cavity.24 25 Sakane and colleagues25 reported that cephalexin preferentially entered the CSF after nasal administration compared to intravenous (IV) and intraduodenal administration in rats. The levels of cephalexin in CSF were 166-fold higher 15 minutes after nasal administration than those of the other two routes. Most recently, studies by Wang and colleagues showed that the ratio of the methotrexate AUCcsp value between the IN route and the IV injection was over 13-fold.26... 

Various transport processes used by low molar mass drugs to cross the epithelial barrier lining oral, buccal, nasal, vaginal, and rectal cavities include passive diffusion, carrier-mediated transfer systems, and selective and nonselective endocytosis. Additionally, polar materials can also diffuse through the tight junctions of epithelial cells (the paraceUular route). Evidence also exists that suggests that macromolecules (particulate... 

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