Effects of microwave on drug release property of poly(methyl vinyl ether-co-maleic acid) matrix

The drug release behavior of beads made of poly(methyl vinyl ether-co-maleic acid) was investigated with respect to the influence of microwave irradiation. The beads were prepared by an extrusion method with sodium diclofenac as a model water-soluble drug. The beads were subjected to microwave irradiation at 80 W for 5 and 20 min, and at 300 W for 1 min 20 s and 5 min 20 s. The profiles of drug dissolution, drug content, drug-polymer interaction, and polymer-polymer interaction were determined by using dissolution testing, drug content assay, differential scanning calorimetry, and Fourier transform infra-red spectroscopy. Keeping the level of supplied irradiation energy identical, treatment of beads by microwave at varying intensities of irradiation did not bring about similar drug release profiles. The extent and rate of drug released from beads were markedly enhanced through treating the samples by microwave at 80 W as a result of loss of polymer-polymer interaction via the (CH(2))(n) moiety, but decreased upon treating the beads by microwave at 300 W following polymer-polymer interaction via the O-H, COOH, and COO(-) moieties as well as drug-polymer interaction via the N-H, O-H, COO(-), and C-O moieties. The beads treated by microwave at 300 W exhibited a higher level of drug release retardation capacity than those that were treated by microwave at 80 W in spite of polymer-polymer interaction via the (CH(2))(n) moiety was similarly reduced in the matrix. The mechanism of drug release of both microwave-treated and untreated beads tended to follow zero order kinetics. The drug release was markedly governed by the state of polymer relaxation of the matrix and was in turn affected by the state of polymer-polymer and/or drug-polymer interaction in beads.