Coated dosage forms for colon-specific drug delivery.

Coating materials used in the manufacture of colon-specific solid oral dosage forms include polymers with a pH-dependent solubility that rely on the difference in pH between the small and the distal large intestine (pH-controlled release), polymers with a slow or pH-dependent rate of swelling, dissolution or erosion that take advantage of the constant small intestinal transit time (time-controlled release), polymers that are degradable by the microbial enzymes in the colon (enzyme-controlled release) and polymers that form firm layers that are destroyed by an increase of the luminal pressure in the colon caused by peristaltic waves (pressure-controlled release). This review gives an overview of coated dosage forms that have been developed to achieve colon specificity.