Novel polymeric excipients for colon‐targeting

Abstract

Oral drug delivery to the colon is of interest for the local treatment of colonic diseases and for the systemic delivery of drugs. Our goal is to develop coating materials that are stable in gastric and small intestinal fluids and degradable in the colon by bacterial polysaccharidases. For testing colon‐degradability an in vitro model was developed. A number of polysaccharide derivatives were synthesized and tested: almost completely ethylated or acetylated galactomannans, polyurethanes with galactomannan sections, crosslinked galactomannans and dextranesters of fatty acids. Generally, degradability decreased with increasing degree of substitution. Especially crosslinked galactomannan and dextranesters with a low degree of substitution or crosslinking, respectively, are promising materials. Using an industrial coating technique tablets were coated with crosslinked galactomannan and the enzymatically induced in vitro dissolution of a model drug was investigated.

Polysaccharides for Colon–Targeted Drug Delivery: Improved Drug–Release Specificity and Therapeutic Benefits

“…The results of both studies showed that this coating was able to protect the drug from being released in the stomach and small intestine, but was degraded by colonic bacterial enzymes (Raghavan et al, 2002). The galactomannans in locust bean gum can be cross-linked, forming a water-insoluble film, which can then be degraded by bacteria in the colon (Hirsch et al, 1995). Locust bean gum galactomannans were crosslinked by 1,4-butanedioldiglycidyl ether, yielding a low crosslinked product that can be used to form films.…”

“…The material was then used to spraycoat theophylline tablets, which were used as a model drug. When placed under conditions representing passage through the small intestine, drug release was observed, but the researchers concluded that the lag time prior to drug release could be increased by applying a thicker coating of the crosslinked galactomannans (Hirsch et al, 1995).…”