Nasal epithelium drug transport across

This refers to the transport across the epithelial cells, which can occur by passive diffusion, carrier-mediated transport, and/or endocytic processes (e.g., transcytosis). Traditionally, the transcellular route of nasal mucosa has been simply viewed as primarily crossing the lipoidal barrier, in which the absorption of a drug is determined by the magnitude of its partition coefficient and molecular size. However, several investigators have reported the lack of linear correlation between penetrant lipophilicity and permeability [9], which implies that cell membranes of nasal epithelium cannot be regarded as a simple lipoidal barrier. Recently, compounds whose transport could not be fully explained by passive simple diffusion have been investigated to test if they could be utilized as specific substrates for various transporters which have been identified in the... 

Lipophilic drug molecules are absorbed across the nasal epithelium by passive transcellular diffusion. For small, unionized molecules, this provides a rapid efficient transport mechanism, often resulting in plasma concentration profiles resembling that of intravenous injection and bioavailabilities of up to 100%. 

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