Formulation Approaches to Colon Delivery: an Overview

Oral colon delivery systems are currently under investigation as a strategy to enable effective and well-tolerated treatments for large bowel pathologies and possibly enhance the intestinal absorption of peptides and proteins. A variety of approaches have been attempted to design and manufacture advanced formulations for site-controlled release to colon. Such approaches are generally based on the use of polymeric coatings or matrices, which may be susceptible to microbial degradation, pH-dependent dissolution or mechanical disruption when the dosage form is positioned in the colon, or simply delay the onset of release throughout the small bowel. Microbiota-activated formulations have primarily been obtained from naturally-occurring polysaccharides in admixture with insoluble structuring excipients. Alternatively, synthetic azo compounds have been employed. pH-sensitive delivery systems are expected to respond to pH changes in the lower intestine, such as the rise generally observed in the terminal ileum and distal colon or the relatively slight acidification of caecal contents by bacterial fermentation products. Pressure-dependent devices would break up as a result of an increase in the intraluminal pressure that solid substrates may perceive in the large intestine. Finally, time-dependent dosage forms are intended to undergo programmed erosion, rupture or enhanced permeability phenomena, thus deferring the onset of release regardless of the aforementioned physiological variables. In this presentation, the overall rationales and strategies behind the design of oral colon delivery systems are outlined and discussed.