Preparation and in vitro evaluation of macrocyclic metronidazole conjugates as an oral colon-specific delivery system

The antimicrobial drug metronidazole (MTZ) was covalently conjugated to the secondary hydroxyl groups of β-cyclodextrin through ester linkage using sodium hydride as the deproton reagent. The preliminary release behavior of MTZ in rat gastrointestinal tract contents was studied at 37 °C within 24 h. In the contents of stomach, the conjugates did hardly release MTZ, released MTZ only 9.5 % in the contents of small intestine, and released MTZ significantly up to 43.6 and 40.2 % in the contents of cecum and colon, respectively. These results indicate that the conjugate activation took place site-specifically in the rat cecal and colonic contents, probably via the biodegradation by glycosidases and hydrolases. The present MTZ-appended cyclodextrin conjugate may be of value as an orally administered delayed-release and/or colon-specific prodrug.