Poly(ethylene oxide) based delivery systems influence of polymer molecular weight and gel viscoelasic behaviour on drug release mechanism

The release kinetics of monolithic drug deliverydevices based on poly(ethylene oxide)(PEO) was investigated. Wter soluble PEO's with molecularweights of 600,000 and 4,000,000 and two blends were studied. the water swelling and dissolution characteristics of the two blends, along with the diffusivity of the drug etofylline in the water-penetrated polymer gels were analyzed. The higher molecular weight PEO and the two blends underwent swelling rather than polymer dissolution. As a result, a non constant release induced by the prevailing diffusive control was observed. Conversely,the drug release from the lower molecular weight PEO was aresult of equal rates of swelling and dissolutn, which gave a constant release rate.