Controlled Drug Delivery via the Nasal Route

Nasal administration is widely used as the logical choice for topical treatment of conditions affecting the nose or paranasal sinuses such as allergic or infectious rhinitis and sinusitis. However, given the rich vascular nature of the nasal mucosa and porous and thin epithelial membrane, the nasal route can also be exploited for systemic drug delivery. It is a promising alternative route for delivering macromolecules, such as peptide and protein drugs and vaccines and is also regarded as a route for delivery of smaller, lower molecular weight drugs that may be subject to first-pass metabolism. In addition, absorption of drug from the olfactory region of the nose provides a potential pathway for drug delivery to the central nervous system (CNS). Nasal administration is less well-suited to the administration of chronic therapies or for those requiring sustained blood levels over time unless they are formulated in a controlled-release system. One strategy to extend delivery times is to decrease the mucociliary clearance (MCC); this can be achieved by increasing the viscosity of the formulation or by enhancing adhesion of the system at the site. This can prolong residence and thus enhance drug absorption. The most common commercially available medicines are solution-based formulations coupled with mucoadhesive systems which may incorporate enzyme inhibitors and nasal permeation enhancers. The first diminishes the enzymatic activity at mucosa, while the latter increases the permeability of the drug, enhances the drug nasal residence time, and improves the therapeutic efficacy of the systemic drugs.