Two basic approaches may be taken in delivering drugs to the colon: time-delayed release or colonic targeting. The former involves sustained release dosage forms, which are designed to prolong drug dissolution and hence absorption, until it reaches the colon. This strategy shows lack of specificity when compared with others that take advantage of unique characteristics present in the colon. Direct targeting involves the exploitation of environmental properties of the colon, like pH of the colon, enzymatic activity or intraluminal pressure. In general, the ideal colonic drug delivery may be accomplished by using pellets, which are known to have more predictable gastric emptying and great colonic residence times, and coated dosage forms with a simple design since they are easy to manufacture. Theoretically, the enzyme dependent systems, and, specially, those based in the use of polysaccharides, are more specific and non-toxic. Nevertheless, any of the others approaches might be suitable to obtain a colonic delivery system with the appropriate characteristics. Some commercially time-dependent and pH-dependent systems have shown important benefits in the treatment of inflammatory bowel disease, despite their less specificity. The investigations in this field should be conducted to identify the appropriate approach, which can result in the delivery of drugs in a safe, effective and less expensive manner with minimum fluctuation in terms of release of drug at target site.
Colon specific delivery; Time-dependent systems; pH-dependent systems; Systems based on the colonic microflora; Systems based on the intraluminal pressure
