Recent approaches for colon drug delivery.

Colon delivery is especially required for drugs intended to act locally or for drugs that exhibit maximum systemic absorption from the colon. However, exposure to extreme pH conditions, gastric enzymes, bile salts and variation in gastric emptying makes the development of colon release dosage forms extremely challenging. The approaches generally used for formulating a colon release dosage form include use of pH dependent release polymers, time-release coatings, prodrugs and biodegradable polymers. Although, considerable choice exists while selecting a pH dependent release polymer, the drug release from these polymers is easily influenced by nature of diet and disease. In addition, while these polymers may prevent drug release in stomach (pH 1-3) and proximal small intestine (pH 6.5), the drug may be prematurely released in vivo in lower small intestine (pH 7.5). Similarly, variation in gastric transit time due to nature of diet and severity of disease often lead to reduced performance of time-release based colon delivery dosage forms. Therefore, new approaches are continuously being evaluated to ensure compliance with requirement of colon release and to reduce the variation in their performance. This article is aimed at studying the recent patents with a view to unveil new concepts being put into use for designing colon release dosage forms.