Development of oral controlled release preparations, a PVA swelling controlled release system (SCRS). I. Design Of SCRS and its release controlling factor.

Polyvinyl alcohol (PVA) is hydrophilic and swells easily by absorbing water. Some grades of PVA, whose degree of hydrolysis is 96.0 and 97.5 mol%, showed volume expansion of 500% by swelling at 37 degrees C. This expansion was inhibited by swelling controlling agents, namely salts. Based on this unique property of PVA, a new type of controlled release system was developed. The release rate was controlled by the content of PVA and a swelling controlling agent in the core tablet, and the composition and coating level of the film. Emedastine difumarate was incorporated into the system. At the initial stage of drug release, the rate of release was determined by the permeation through the membrane - a mixture of ethylcellulose and hydroxypropyl methylcellulose. After the membrane burst by the swelling of PVA, the release rate was controlled by the PVA matrix. Release patterns of zero-order, two phase zero-order, and rapid release after lag-time were obtained with this system.