Pectin/chitosan mixtures as coatings for colon-specific drug delivery:: an in vitro evaluation

The ability of a multiple-unit dosage form to reach the colon intact has been investigated, in vitro, using conditions chosen to simulate the pH and times likely to be encountered during transit to the colon. Small tablets were coated with either pectin USP or pectin in a 1:10 mixture with chitosan. Indomethacin and paracetamol were used as model drugs to represent poorly soluble and soluble compounds. Pectin alone was able to protect the cores from premature release, but only when a substantially thick coat was present. Pectin/chitosan mixtures achieved better protection at a lower coat weight. The use of pectinolytic enzymes to simulate breakdown in the colon showed that the pectin/chitosan mixture was susceptible to enzymic breakdown and allowed drug release to occur. The importance of pre-exposure of the tablets to conditions in the upper gastro-intestinal tract prior to exposure to the enzyme was noted. (C) 1998 Elsevier Science B.V. All rights reserved.