Novel pH-sensitive hydrogels for colon-specific drug delivery.

The purpose of this study is to develop novel intestinal specific drug delivery systems with pH-sensitive swelling and drug release properties. Acryloyl ester of 5-[4-(hydroxy phenyl) azo] salicylic acid (HPAS) as an azo derivative of 5-amino salicylic acid (5-ASA) was prepared under mild conditions. The HPAS was covalently linked with acryloyl chloride, abbreviated as APAS. Cubane-1,4-dicarboxylic acid (CDA), linked to two 2-hydroxyethyl methacrylate (HEMA) groups, was the cross-linking agent (CA). Methacrylic-type polymeric prodrugs were synthesized by free radical copolymerization of methacrylic acid, poly(ethyleneglycol monomethyl ether methacrylate), and APAS in the presence of cubane cross-linking agent. The effect of copolymer composition on the swelling behavior and hydrolytic degradation were studied in simulated gastric (SGF, pH 1) and intestinal fluids (SIF, pH 7.4). The composition of the cross-linked three-dimensional polymers was determined by FTIR spectroscopy. The hydrolysis of drug-polymer conjugates was carried out in cellophane membrane dialysis bags containing aqueous buffer solutions (pH 1 and pH 7.4) at 37 degrees C. Detection of the hydrolysis product by UV spectroscopy shows that the azo prodrug (HPAS) was released by hydrolysis of the ester bond located between the HPAS and the polymer chain. Drug release studies showed that the increasing content of MAA in the copolymer enhances hydrolysis in SIF. These results suggest that pH-sensitive systems could be useful for preparation of a muccoadhesive system and controlled release of HPAS as an azo derivative of 5-amino salicylic acid (5-ASA).