The use of polysaccharides to target drugs to the colon

Targeting pharmaceutical drugs to the colon makes it possible to guarantee local or systemic drug delivery to this site. To deliver the compounds in a non-degraded form to the last part of the gastrointestinal tract, they must first of all pass through the stomach, the upper part of the intestine and must use the characteristics of the colon to specifically release the drugs in this part of the digestive tract. Usual methods for the specific delivery of drugs to the colon are based on the chemical or technological modification of excipients. Among these, pH-dependent coatings or those degraded specifically by the colonic microflora make it possible to create dosage forms containing high levels of drugs compared to matrix or hydrogel systems. Nevertheless, inter- and intra-individual variations in gut pH and in transit time along the gastrointestinal tract can stand in the way of specific drug delivery. To improve the specificity of drug release, certain types of polysaccharides can be used to create the dosage forms. These excipients are specifically degraded by the colonic microflora and have been used as polymer drug conjugates, coatings and matrix agents. However, most of these compounds are strongly hydrophilic leading to premature release. For these reasons, some polysaccharides, such as inulin, amylose, guar gum and pectins, have been chemically modified to increase their hydrophobicity or have been combined with other conventional hydrophobic polymers. This article reviews the potential uses of polysaccharides, the limits and the future developments in this field with these natural polymers. (C) 2002 Elsevier Science Ltd. All rights reserved.