Nasal Physiology

Various aspects of nasal physiology and mechanisms, such as nasal anatomy, resistance, airflow, and the nasal cycle may have a potential impact on IN delivery. Relevant reviews can be found elsewhere (51,52). Briefly, the nasal cavity is separated by the nasal septum (comprised of cartilage and bone), with each half opening at the face (via the nostrils). In addition, the nasopharynx provides a connection to the oral cavity. The olfactory region, the respiratory region, and the anterior and posterior vestibules are the three major areas of the nasal cavity. The lateral walls contain a folded structure, referred to as the conchae. This structure is further divided into the superior, median, and inferior turbinates, giving a total surface area, in humans, of approximately 150 cm2.

Epithelial tissue in the nasal cavity is highly vascularized, providing a promising conduit for drug delivery. The cellular composition of the nasal

FIGURE 1 Galantamine pharmacokinetics in dogs given intranasal formulation (filled diamonds), oral solution (filled triangles), and oral tablet (filled squares). The data are shown for galantamine measured in (A) plasma; (B) the CSF; and (C) as the ratio of drug measured in CSF to plasma.

FIGURE 1 Galantamine pharmacokinetics in dogs given intranasal formulation (filled diamonds), oral solution (filled triangles), and oral tablet (filled squares). The data are shown for galantamine measured in (A) plasma; (B) the CSF; and (C) as the ratio of drug measured in CSF to plasma.

FIGURE 1 (Continued)

epithelial tissue consists primarily of basal cells, goblet cells, ciliated columnar cells, and nonciliated columnar cells, with varying proportions throughout different regions of the nasal cavity. Basal cells are poorly differentiated and operate as stem cells to replace other epithelial cells. Goblet cells contain an abundance of secretory granules filled with mucin and produce secretions that form the mucus layer. Ciliated cells aid in the transport of mucus to the nasopharynx.

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