Dynamic release of riboflavin from a colon-targeted delivery device: an in vitro study

Drug loaded cylindrical devices, composed of poly(N-vinyl-2-pyrrolidone) and poly(acrylamide-co-itaconic acid), have been synthesized and release of vitamin B-2 form these gels has been studied as a function of pH of the release media, initial of the drug, thickness of the gels, and amount of monomer acid present in the gels. The devices showed a strong loading pH-dependent release behavior, thus exhibiting maximum release at pH 7.4. Similarly, the amount of drug released was found to increase with initial load. A linear dependency was observed between t(1/2) values (time required for 50% release) and square of the diameter of the devices, thus supporting the Tanaka-Fillmore theory. Amount of itaconic acid present in the device affected the release dynamics in a rather interesting way. The amount of drug released was found to increase with acid content up to 15.3 mM and then started decreasing. This was explained on the basis of decrease in the swelling of the device due to formation of a complex structure through H-bonding interactions between non-ionized COOH groups and an-tide groups. The different release behavior, exhibited by device in the acidic and slightly alkaline pH, has been explained on the basis of two different mechanism. Finally, as the device demonstrates maximum drug release in the media of pH 7.4, it has the potential to be used for colon-targeted drug delivery. (C) 2003 Elsevier Science B.V. All rights reserved.