Amylose as a coating for drug delivery to the colon: Preparation and in vitro evaluation using 5-aminosalicylic acid pellets

Colon-specific drug delivery may be possible by the application of dried amylose films to pharmaceutical formulations. Amylose, one of the major fractions of starch, possesses the ability to form films through gelation, when prepared under appropriate conditions. The microstructure of the film is potentially resistant to the action of pancreatic cu-amylase but is digested by amylases of the colonic microflora. However, under simulated gastro-intestinal conditions, coatings made solely of amylose swell, become porous and allow drug release, Incorporation of insoluble polymers into the amylose film, to control amylose swelling, provides a solution to this problem. A range of cellulose and acrylate based copolymers were assessed, of which a commercially available ethylcellulose (Ethocel(R)) was found to control the swelling most effectively. The in vitro dissolution of various coated pellets under simulated gastric and small intestinal conditions, using commercially available pepsin and pancreatin, was determined and demonstrated the resistance of the amylose-Ethocel(R) coat (1:4 w/w) to such conditions over a period of 12 h. With additional thermal treatment of the coat, in vitro drug release under simulated gastric and small intestinal conditions was prevented further, even after storage of the product for one year. Coated pellets were further evaluated in a batch culture fermenter, simulating colon conditions, containing an inoculum of mixed faecal bacteria. The in vitro release of 5-aminosalicylic acid from coated pellets in the fermenter system was shown to occur.