Development of an azopolymer based colonic release capsule for delivering proteins/macromolecules

The colon, high in microbial contents with degradation ability of azo bonds, seems to be suitable for site-specific delivery of drugs. The degradation of azoaromatic hydrogel depends on the degree of swelling. However, the degree of swelling of azopolymers and the ability of the azoaromatic polymers to protect peptide drugs against the action of digestive enzymes still remains to be established. An azopolymer was synthesized and membranes were cast to investigate the degree of swelling. An azopolymer-coated capsule suitable for delivering peptides/proteins to the colon was developed by in vitro evaluation using vitamin B12 as a model drug to screen various formulations. For in vitro dissolution the half-changed method was used to mimic the pH-time profile in the GI tract. It was shown that the release of vitamin B12 is dependent on the degree of swelling which increases as pH increases. An in vivo study was also performed with insulin in azopolymer-coated capsules in 6 normal beagle dogs. The results suggest that this azopolymer-coated capsule is capable of protecting peptide/macromolecules against digestive enzymes. However, to obtain a promising peroral insulin capsule, more formulation work is required to achieve better absorption availability.