Design of controlled-release solid dosage forms of alginate and chitosan using microwave
The influence of microwave irradiation on the drug release properties of alginate, alginate–chitosan and chitosan beads was investigated. The beads were prepared with the highest possible concentration of polymer by an extrusion method. Sulphathiazole was selected as a model drug. The beads were subjected to microwave irradiation at various combinations of irradiation power and time. The profiles of drug dissolution, drug content, drug stability, drug polymorphism, drug–polymer interaction, polymer crosslinkage and complexation were determined by dissolution testing, drug content assay, differential scanning calorimetry (DSC) and fourier transform infra-red spectroscopy (FTIR). The chemical stability of the drug entrapped in the beads was unaffected by the microwave irradiation. However, the drug in the chitosan beads underwent polymorphic changes. Polymorphic changes were prevented by means of drug–alginate interaction in alginate and alginate–chitosan beads. Changes in the polymorphic state of drug were found to have insignificant effect on the drug release profiles of chitosan beads. The release-retarding property of alginate and alginate–chitosan beads was significantly enhanced by subjecting the beads to microwave irradiation. Positively charged calcium ions and chitosan are known to interact with negatively charged alginate. DSC and FTIR analyses indicated that the reduction in rate and extent of drug released from the treated beads was primarily due to additional formation of non-ionic bonds, involving alginate crosslinkage and alginate–chitosan complexation. The results showed that microwave technology can be employed in the design of solid dosage forms for controlled-release application without the use of noxious chemical agents.