Abstract
Colonic drug absorption, as an alternative to parenteral drug delivery, is evaluated for its potential advantages and limitations. Methodologies for studying and enhancing colonic drug absorption are discussed with emphasis on the biological and chemical nature of absorption barriers. Recent efforts at identifying factors that control colonic drug absorption and which might be exploited in a delivery scheme are described. 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. Solid formulations intended for targeted drug release into the lower gastrointestinal (GI) tract are beneficial for the localized treatment of several diseases and conditions, mainly inflammatory bowel diseases, irritable bowel syndrome and colon cancer. Also, because of their inherent potential to delay or avoid systemic drug absorption from the small intestine, colonic formulations can be utilized for chronotherapy of diseases which are affected by circadian biorhythms (e.g., asthma, hypertension and arthritis), and to achieve clinically relevant bioavailability of drugs that are poorly absorbed from the upper parts of the GI tract because of their polar nature and/or susceptibility to chemical and enzymatic degradation in the small intestine (e.g., proteins and peptides).
