Exploiting gastrointestinal bacteria to target drugs to the colon: an in vitro study using amylose coated tablets

The bacterial substrate amorphous amylose, in the form of a film coating, provides a means of delivering drugs to the colon. This coating has traditionally been applied to multi-unit systems, in part because of the small size and divided nature of this type of dosage form, which provides a large surface area for enzymatic attack and drug release. The present study was conducted to explore the utility of the coating for colonic targeting of single unit tablet systems. Amylose was combined with the water-insoluble polymer ethylcellulose, which acts as a structuring agent, in different proportions to produce film coatings of various thicknesses for application to mesalazine (mesalamine or 5-aminosalicylic acid)-containing tablets. Drug release from the coated products was assessed under pH dissolution conditions resembling the stomach and small intestine, and also in conditions simulating the colon using a batch culture fermenter inoculated with human faecal bacteria. The rate and extent of drug release was related to the ratio of amylose to ethylcellulose in the film and the thickness of the coating. Increasing the proportion of ethylcellulose in the film and/or the thickness of the coating depressed the rate of drug release in the conditions of the upper gastrointestinal tract. Drug release from the coated products was accelerated in the fermentation environment of the colon. This is attributed to bacterial digestion of the amylose component of the film coat producing pores for drug diffusion. This work indicates that amylose coated tablet formulations are promising vehicles for drug delivery to the colon.