Polysaccharides Based Colon Specific Drug delivery: A Review

Although oral delivery has become a widely accepted route of administration of therapeutic drugs, the gastrointestinal tract presents several formidable barriers to drug delivery. The delivery of drugs to the colon has a number of therapeutic implications in the field of drug delivery. In the recent times, the colon specific delivery systems are also gaining importance not only for local drug delivery of drugs but also for the systemic delivery of protein and peptide drugs. The various approaches that can be exploited to target the release of drug to colon include prodrug formation, coating with pH sensitive polymers, coating with biodegradable polymers, embedding in biodegradable matrices, hydrogel, timed release systems, osmotic and bioadhesive systems. In this review article we have made an attempt to give an overview on polysaccharide-based colon specific drug delivery system. Key Word: Polysaccharide, Gastrointestinal tract, Hydrogel. INTRODUCTION: The oral route is considered to be most convenient for administration of drugs to patients. The conventional oral dosage forms normally dissolve in the stomach fluid or intestinal fluid and are absorbed from these regions of the Gastrointestinal Tract (GIT), which depend upon the physicochemical properties of the drug. Localized delivery of the drugs in the colon region is possible only when the drug is protected from the hostile environment of upper GIT. Dosage forms that deliver drugs into the colon region rather than upper GIT proffers number of advantages. Oral delivery of drugs to the colon is valuable in the treatment of diseases of colon (ulcerative colitis, Chron's disease, carcinomas and infections) whereby high local concentration can be achieved while minimizing side effects that occur because of release of drugs in the upper GIT or unnecessary systemic absorption. The colon is rich in lymphoid tissue.Uptake of antigens into the mast cells of the colonic mucosa produces rapid local production of antibodies and this helps in efficient vaccine delivery. Specific systemic absorption of drugs and protein/peptides in the colonic region offers interesting possibilities for the treatment of disease susceptible to diurnal rhythm such as asthma, arthritis or inflammation. The colon is considered to be more suitable for delivery of peptides and protein in comparison to small intestine . Besides this low hostile environment, the colonic transit time (20-30 hours) and the colonic tissue is highly responsive to the action of absorption enhancers . Colonic delivery can be accomplished by oral or rectal administration. Rectal dosage forms such as suppositories and enemas are not always effective since a high variability in the distribution of these forms is observed .The GIT is divided into various regions like stomach, small intestine and large intestine. The colon serves four major functions: viz; creation of suitable environment for the growth of colonic microorganisms, storage reservoir of faecal contents, expulsion of the contents of the colon at an appropriate time, absorption of potassium and water from lumen and excretion of potassium and bicarbonate. An overview of the pH details of the GIT is shown in Table 1. Gastric emptying of dosage forms is highly variable and depends primarily on whether the subject is fed or fasted and on the properties of the dosage form such as size and density. The transit times of small dosage forms in GI tract is shown in Table 2. TABLE1: AVERAGE PH IN THE GIT Location pH Oral cavity 6.2-7.4 Oesophagus 5.0-6.0 Stomach Fasted condition: 1.5-2.0 Fed condition: 3.0-5.0 Small intestine Jejunum: 5.0-6.5 Ileum: 6.0-7.5 Large intestine Right colon: 6.4 Mild colon and left colon: 6.0-7.6 Ravi Kumar et al /Int.J. PharmTech Res.2009,1(2) 335 Organ Transit time( h) Stomach <1 (Fasting) >3 ( Fed)