Nasal transmucosal and transdermal delivery systems

A nasal-based biopharmaceutical delivery route is considered potentially attractive as:

• it is easily accessible;

• nasal cavities are serviced by a high density of blood vessels;

• nasal microvilli generate a large potential absorption surface area;

• nasal delivery ensures the drug bypasses first-pass metabolism. However, the route does display some disadvantages, including:

• clearance of a proportion of administered drug occurs due to its deposition upon the nasal mucous blanket, which is constantly cleared by ciliary action;

• the existence of extracellular nasal proteases/peptidases;

• low uptake rates for larger peptides/polypeptides.

Peptide/protein uptake rates across the nasal epithelia are dependent upon molecular mass. Relatively small peptides (such as oxytocin, desmopressin and luteinizing hormone-releasing hormone analogues) cross relatively easily, and several such products used medically are routinely delivered nasally. Larger molecules (of molecular mass greater than 10 kDa) generally do not cross the epithelial barrier without the concurrent administration of detergent-like uptake enhancers. Long-term use of enhancers is prohibited due to their damaging cellular effects.

Research efforts also continue to explore mucosal delivery of peptides/proteins via the buccal, vaginal and rectal routes. Again, bioavailabilities recorded are low, with modest increases observed upon inclusion of permeation enhancers. Additional barriers also exist relating, for example, to low surface areas, relatively rapid clearance from the mouth (buccal) cavity and the cyclic changes characteristic of vaginal tissue. Various strategies have been adopted in an attempt to achieve biopharmaceutical delivery across the skin (transdermal systems). Most have met with, at best, modest success thus far. Strategies employed include the use of a jet of helium or the application of a low voltage to accelerate proteins through the skin.

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