Mechanism of medicine release from solid dispersion composed of poly(ethylene oxide) carboxyvinylpolymer interpolymer complex and pH effect on medicine release

Solid dispersion composed of the poly(ethylene oxide) (PEO)-carboxyvinylpolymer (CP) interpolymer complex containing phenacetin (PHE) was prepared using water/ethanol (1/1, v/v) mixture as a solvent. The release mechanism of PHE from the solid dispersion and the effect of pH on PHE release were studied. The physicochemical properties of the solid dispersion were analyzed by powder X-ray diffractometry, thermal analysis and IR spectroscopy. Transmittance of the polymer solution was measured to study the complexation between PEO and CP. The degree of PEO-CP complex formation by hydrogen bonding varied depending on the PEO/CP ratio. It was found that the PHE release from the solid dispersion was controlled by the degree of the complex formation. With PHE powder, the effect of pH on the dissolution behavior was hardly observed. In contrast, the release rate from the solid dispersion increased with a higher pH. This result is probably caused by the fact that the PEO-CP complex is broken at a higher pH. (C) 1998 Elsevier Science B.V. All rights reserved.