Bioadhesion: new possibilities for drug administration?

Bioadhesion (and mucoadhesion) is the process whereby synthetic and natural macromolecules adhere to mucosal surfaces in the body. If these materials are then incorporated into pharmaceutical formulations, drug absorption by mucosal cells may be enhanced or the drug released at the site for an extended period of time. For synthetic polymers, such as the chitosans, carbopols and carbomers, the mechanism of bio/mucoadhesion is the result of a number of different physicochemical interactions. Biological bio/mucoadhesives, such as plant lectins, show specific interactions with cell surfaces and mucin and are seen as the 'second generation' bioadhesives. Bioadhesive systems for drug administration via the buccal and nasal cavities are nearing the market; in the case of nasal bioadhesion, bioadhesive microparticles are used. A bioadhesive formulation for drug administration to the vagina is in use. The gastrointestinal tract is proving a more difficult site because of the rapid turnover of mucus, and relatively constant transit time, but intensive research is in progress. Micro- and nano-particles, coated with either bio/mucoadhesive polymers or specific biological bioadhesives, are showing some promise, but will require considerable research and development before reaching the market.