Colon Targeted Drug Delivery: Current and Novel Perspectives

In general, we know that small intestine is mostly the site for drug absorption but in some cases the drug needs to be targeted to some other sites for absorption due to various factors like any disease condition, degradation related situations, for sustained release of drugs etc. Colon targeted drug delivery is a relatively new concept for the absorption of drugs as it offers near neutral pH. Also it offers long residence time, thereby increasing the drug absorption. The nature of food and enzymes does not affect the drug absorption. Colon has proved to be a site for the absorption of poorly soluble drugs. For the successful targeting of drugs to colon the dosage form should be designed such that it prevents the drug release in upper GIT and releasing it in the colonic region. This review article comprises of the various aspects of colon targeting which we should know before experimenting the technique and their IVIVC using recent evaluation models through x-ray imaging and gamma-scintigrapy. INTRODUCTION: The human GI tract is the union of stomach, small intestine and large intestine. Colon is the part of large intestine which starts from the ileocaecal junction to the anus. Colon, rectum and anal canal are the main parts of large intestine. Colon itself is composed of units named caecum, ascending colon, transverse colon, rectum and anal canal. The ascending and descending colon have peritoneal folds which are also called as mesenteries. The histological profile of colon is the longitudinal muscle fibre, submucosal layer, mucous lining one over another. Superior and inferior mesenteric arteries are there for the supply of blood to the colon. The image depicting the colon anatomy is below. A big amount of micro flora is found in colon which plays a very important role in the metabolic process undergoing in the intestinal region. The microorganisms find colon as a suitable place for their growth. Colon is a storage site of fecal contents and it also has a very high absorption capacity. Oral route of dosage form administration is the convenient and most commonly used route for colonic drug delivery due to various advantages it offers in contrast to other routes of drug administration . Rectal route of drug administration is also found to be shortest route for targeting drug to colon. Although approaching the proximal part of colon is not easy via rectal route of administration. Rectal administration of drug offers less compliance and is also uncomfortable for patients . Colonic diseases such as ulcerative colitis, crohn’s disease, colon cancer, amebiosis require local therapy and also the systemic delivery of proteins and peptides is achieved by development of locally acting colon targeted drug delivery system as shown in the figure 1. The proteins and peptides drugs gets inactivated and destroyed in the acidic environment of stomach and in the presence of pancreatic enzyme .