Colonic drug delivery: prodrug approach.

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. One of the approaches used for colon specific drug delivery is the formation of a prodrug 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 (e.g. azoreductase, glucuronidase, glycosidase, dextranase, esterase, nitroreductase, cyclodextranase, etc.). The present review includes varius prodrug approaches investigated for colon drug delivery and their site specificity.