Coated pellets for oral colon delivery

Because of their spherical or pseudo-spherical shape, uniform size and smooth surface, pellets are of particular interest for use as cores in the manufacturing of coated oral delivery systems. When intended for colon delivery, pellet formulations may be provided with enzymatically-degradable, pH-sensitive or time-controlled polymer coatings. While layers that are liable to microbial breakdown or pH-dependent dissolution would enable targeted release as triggered by physiological characteristics of the environment where the drug is intended to be delivered, time-based coats possess an intrinsic ability to defer its release throughout the small intestinal transit of the dosage form irrespective of regional differences in terms of pH, microbial population and other variables. Rupturable, erodible and permeable coats have been described for time-based colonic release. According to their formulation strategies, coated pellets that have been proposed for colon delivery are reviewed and discussed in the present article.