Review Article Indian J. Pharm. Biol. Res Vol. 1 (3), Sep., 2013 ISSN:2320-9267 *Corresponding Author: Ritesh Kumar, Associate Professor, Department of Pharmaceutics, College of Pharmacy, Agra (U.P), India. E-Mail Id: ritesh_pharma@rediffmail.com 67 1* College of Pharmacy, Agra, Uttar Pradesh, India. 2 Amity Institute of Pharmacy, Amity University, Noida, Uttar Pradesh, India. 3 Department of Pharmacy, S. N. Medical College, Agra, Uttar Pradesh, India. Received 11-07-2013; Revised 18-07-2013; Accepted 27-07-2013 ……………………………………………………………………………………………………… Abstract The colon is a site where both local and systemic delivery of drugs can take place. Local delivery allows topical treatment of inflammatory bowel disease. However, treatment can be made effective if the drugs can be targeted directly into the colon, thereby reducing the systemic side effects. This review mainly describes the primary approaches for CDDS (Colon Specific Drug Delivery) namely prodrugs, pH and time dependent systems, and microbially triggered systems, which achieved limited success and had limitations as compared with newer CDDS namely pressure controlled colonic delivery capsules. Oral administration of different dosage forms is the most commonly used method due to flexibility in design of dosage form and high patient acceptance, but the gastrointestinal tract presents several formidable barriers to drug delivery. In oral colon-specific drug delivery system, colon has a large amount of lymphoma tissue (facilitates direct absorption in to the blood), negligible brush boarder membrane activity, and much less pancreatic enzymatic activity as compared with the small intestine. Colon-specific drug delivery has gained increased importance not just for the delivery of the drugs for treatment of local diseases associated with the colon but also for its potential for the delivery of proteins and therapeutic peptides. Different approaches are designed based on prodrug formulation, pH-sensitivity, time-dependency (lag time), microbial degradation and osmotic pressure etc to formulate the different dosage forms like tablets, capsules, multiparticulates, microspheres, liposomes for colon targeting. 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. This review updated the research on different approaches formulation and evaluation of colon-specific drug delivery. Keywords: Colon, Drug delivery system, Microbial degradation, Osmotic Pressure, Prodrug. …………………………………………………………………………………………………………………………….. 1. Introduction Now a day, various routes of administration have been explored for the effective delivery of the drug. The oral route is considered to be most convenient for the administration of drugs to patients [1]. Oral delivery of drugs in the colon is valuable in the treatment of diseases of colon (colon cancer, ulcerative colitis, crohn's disease and inflammatory bowel disease) whereby high local concentration can be achieved while minimizing side effects. The colon is attracting interest as a site where poorly absorbed drug molecule may have an improved bioavailability. Additionally, the colon has a long retention time and appears highly responsible to agents that enhance the absorption of poorly absorbed drugs. The simplest method for targeting of drugs to the colon is to obtain slower release rates or longer release periods by the application of thicker layers of conventional enteric coating or extremely slow releasing matrices [2]. Modified Approaches for Colon Specific Drug Delivery System: A Review Ritesh Kumar 1* , Amrish Chandra 2 , Pawan Kumar Gautam 3