A Novel Prodrug Approach in Colonic Drug Delivery System

The drug delivery method is chosen based upon the physiological properties of drug, the desired site of action, the biological barrier including drug metabolism that must be overcome to deliver the drug. Prodrugs are continuously being developed as many of the new drugs have low solubility and degradation against enzymatic acid catalyzed breakdown in the human body. Prodrugs are the means of enhancing the therapeutic benefit of drug controlling the pharmacokinetics, pharmacodynamics, non specific toxicity immunogenicity and efficacy. One of the approaches used for colon specific drug delivery is the formation of prodrugs which optimizes drug delivery and improves drug efficacy. Many prodrugs have been evaluated for colon drug delivery. These prodrugs are designed to pass intact and unabsorbed from the upper GIT and undergo biotransformation in the colon releasing the active drug molecule. This biotransformation is carried out by a variety of enzymes, mainly of bacterial origin present in the colon. The colon is largely being investigated as a site for administration of protein and peptides, which are degraded by digestive enzymes in the upper GIT. Also for local diseases of the colon, drug administration to the site of action can not only reduce the dose to be administered, but also decrease the side effects. Technical difficulties faced in preparation of other types of colon specific delivery systems, like coated, multiple coated, systems etc., can be avoided. These approaches have also been used to target various other drugs molecules to the colon to improve the absorption characteristics of these drugs. These include coating with biodegradable polymers, coating with pH-sensitive polymers, time dependent formulations, forming biodegradable matrices, and forming a prodrugs. The present review includes various prodrugs approaches investigated for colon drug delivery.