APPLICATION OF THE SOLID DISPERSION METHOD TO THE CONTROLLED-RELEASE OF MEDICINE .8. MEDICINE RELEASE AND VISCOSITY OF THE HYDROGEL OF A WATER-SOLUBLE POLYMER IN A 3-COMPONENT SOLID DISPERSION SYSTEM

Solid dispersions were prepared with a highly water-soluble medicine ( oxprenolol hydrochloride (OXP)), water-insoluble ethylcellulose (EC) a nd four grades of water-soluble hydroxypropylcellulose (HPC) having di fferent molecular weights. The effects of the composition ratio within the range of 5% of HPC and of the viscosity of HPC hydrogels on the r elease of OXP were studied, The bulk viscosity of HPC hydrogels was ev aluated from the relationship between shear rate and shear stress, The microscopic viscosity was evaluated by the spin probe method of the e lectron spin resonance (ESR) technique. The release rate of OXP decrea sed with increasing HPC composition ratio and became almost constant a t the HPC composition ratio of 3% and more. This result suggests that the release of OXP will occur through its diffusion into the swollen H PC gel phase formed in a solid dispersion at the HPC composition ratio of 3% and more, The bulk viscosity of HPC hydrogels markedly increase d with increasing molecular weight of HPC, but there was little notice able change in release rate and activation energy for the diffusion of OXP. This result can be explained by the fact that the microscopic vi scosity was hardly affected by the molecular weight of HPC, suggesting that the resistance to diffusion of OXP into the swollen HPC gel phas e in the solid dispersion was almost the same regardless of the molecl ar weight of HPC.