Rational design and development of colon-specific prodrugs

Earlier colon was considered as a black-box, acting as a site for production and temporary storage of excreta and responsible for absorption of electrolytes and water. But, with the discovery of sulfasalazine as colon-specific prodrug, the promising and challenging issue of treating local pathologies was presented with colon as an organ of significance for target-specific delivery of drugs. The need and desirable attributes of colon-specific drug delivery systems have been well recognized, extensively explored and documented in the literature. The success of a colon-specific prodrug depends on its rational design and understanding the demands of the organ to be targeted and the delivery system to be developed. The present review mainly focuses on anatomy/physiology of colon, colonic microbiota, enzymatic set up of colon, pathophysiology of local diseases of colon, factors, obstacles and rationale for designing colon specific drug delivery system, various targets, potential drug candidates and novel colon-targeting carriers along with varied linkages that could be explored, merits and demerits of this design and recent trends in this field. Brief review of methodologies for characterization and in vitro/in vivo release studies is presented. The available animal models with quantifying parameters for evaluating colon-targeting potential and effectiveness of the colon-specific prodrugs for inflammatory bowel disease is also included in this review.