Development and in-vitro evaluation of a colon-specific controlled release drug delivery system.

The major challenges in targeting drug to various parts of the gastrointestinal tract include control of drug release with respect to its environment and transit time. These two variables should be taken into consideration in designing a rational colonic drug delivery system. To this end, a swelling matrix core containing pectin, hydroxypropyl methylcellulose (HPMC), microcrystalline cellulose and 5-aminosalicylic acid was developed. This was subjected to a dual coating operation: an inner pH-sensitive enteric and an outer semi-permeable membrane coat with a pore former. In-vitro dissolution studies were carried out in USP apparatus-I using sequential pH media. The first 2 h of dissolution studies were done in HCl buffer at pH 1.5, the next 2 h in pH 5.5 and, finally, in phosphate buffer at pH 6.8 with and without pectinolytic enzyme present. Less than 2% drug was released in the first 6 h and about 90% released in the following 12 h in a controlled manner. The stability studies of the coated systems were performed for 90 days under various conditions and it was found that drug release was not adversely affected. Results indicate that this delivery system has potential for site-specific delivery of drugs to the colon irrespective of transit time and rapid changes in the proximal pH of the gastrointestinal tract.