Colonic drug-targeting: In vitro release of ibuprofen from capsules coated with poly(ether-ester) azopolymers

For the purpose of colonic drug-targeting, poly(ether-ester) azopolymers were synthesized and used to coat capsules containing ibuprofen. The release of ibuprofen was studied from coated capsules incubated in the medium prepared by suspending rat caecal contents in phosphate buffer pH 6.8 (RCCRM) and in capsules incubated in plain phosphate buffer (PB). The release of ibuprofen was higher in RCCRM than in PB. This was due to the presence of azoreductase in RCCRM, an enzyme which breaks down azopolymers by reducing azo bonds. Furthermore, the release of ibuprofen was a function of the thickness of the coating, the release being higher the thinner the coating. Addition of polyethylene glycol in the coating solution resulted in capsules with a higher drug release due to enhanced hydrophilicity of the coating. A two-layer coating gave a too early release, while a thick four-layer coating impeded drug release for 24 h. Medium thickness poly(ether-ester) coating containing 15% polyethylene glycol exhibited potential usefulness in colon-targeting of drugs.