Table 1.

Description of factors affecting intranasal delivery.

Factor	Summary	References
Mucus	Negatively charged gel reduces movement of large, charged, and nonpolar molecules	[34,35,36,37]
Enzymatic degradation	Antimicrobial and other enzymes in mucus and epithelial cells degrade the drug	[36]
Ciliary clearance	Ciliary turnover of mucus will remove slowly diffusing drugs	[38]
Tight junctions	Apical proteins greatly restrict drug movement across epithelium between cells	[39,40,41,42,43,44]
Intrinsic drug characteristics	Molecule weight over 1 kDa, polarity, strong charge can affect absorption	[45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60]
Formulation factors	pH, buffer capacity, osmolarity, and volume are important for liquids. Solubility is additionally important for powders	[61,62,63]
Vasculature and Lymphatics drainage	Vasculature of lamina propria can drain away drug before transport into the CNS	[64]