Polysaccharide drug delivery systems based on pectin and chitosan.

Chitosans and pectins are natural polysaccharides which show great potential in drug delivery systems. Chitosans are a family of strongly polycationic derivatives of poly-N-acetyl-D-glucosamine. This positive charge is very important in chitosan drug delivery systems as it plays a very important role in mucoadhesion (adhesion to the mucosal surface). Other chitosan based drug delivery systems involve complexation with ligands to form chitosan nanoparticles with can be used to encapsulate active compounds. Pectins are made of several structural elements the most important of which are the homogalacturonan (HG) and type I rhamnogalacturonan (RG-I) regions often described in simplified terms as the "smooth" and "hairy" regions respectively. Pectin HG regions consist of poly-glacturonic acid residues which can be partially methyl esterified. Pectins with a degree of methyl esterification (DM) > 50% are known as high methoxyl (HM) pectins and consequently low methoxyl (LM) pectins have a DM less than 50%. Low methoxyl pectins are of particular interest in drug delivery as they can form gels with calcium ion (Ca2+) which has potential applications especially in nasal formulations. In this chapter we will discuss the physicochemical properties of both chitosans and pectins and how these translate to current and potential drug delivery systems.