Colon targeted drug delivery by using natural Polysaccharides/Polymers

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Colonic drug delivery has gained increased importance not just for the delivery of drugs for the treatment of local diseases of colon such as irritable bowel syndrome, inflammatory bowel disease (IBD) including Crohn’s disease and ulcerative colitis but also for its potential for the delivery of proteins and therapeutic peptides like insulin. Recently colon has emerged as a potential site which offers distinct advantages on account of a near neutral pH, a much longer transit time, reduced digestive enzymatic activity, much greater response to absorption enhancers, and the presence of large amounts of enzymes for polysaccharides (e.g., β-D-glucosidase, β-D-galactosidase, amylase, pectinase, xylase, dextranase, etc.) which were secreted by a large number and variety of colonic bacteria. Most of the systems which have been developed for colonspecific drug delivery till date includes coating with pH-sensitive polymers, covalent linkage of a drug with a carrier, time dependent release systems, and enzymatically controlled delivery systems. Enteric coated systems, though they are the most commonly used for colonic drug delivery systems do not allow reproducible drug release. The disadvantage of this system is that the pH difference between small intestine and colon is not being very pronounced. Moreover, the limitation of time dependent release system is that it is not able to sense any variation in the upper gastro-intestinal tract transit time, any variation in gastric emptying time may lead to drug release in small intestine before arrival to colon. Therefore, the most convenient approach known for site-specific drug delivery to colon is enzymatically controlled delivery systems. No drug release can occur unless the system arrives to the colon. Many protein and peptide drugs like insulin, cannot be administered through the oral route because of their degradation by the digestive enzymes of the stomach and the small intestine. To improve the specificity of drug release, certain types of neutral polysaccharides (e.g., pectin, xanthin gum chitosan, dextran, guar gum, and inulin) can be used to create the enzymatically controlled delivery systems. To reach the colon and to be able to specifically deliver a peptide or a protein drug, the dosage form must be formulated taking into account the obstacles of upper gastro-intestinal tract and advantages of colonic environment.

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