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SynopsisThe kinetics of drug release from a series of partial esters of vinyl acetate-maleic anhydride has been investigated. These polymers in their un-ionized forms are hydrophobic and water insoluble, but in their ionized forms they are water soluble. Polymer dissolution is pH sensitive, and different half-esters have a characteristic pH range above which they are soluble and below which they are insoluble. When films are placed in buffered media, they erode a t a constant rate that depends on the pH of dissolution of the polymer and on the pH of the buffered medium. Dissolution of the polymer is limited to the polymer-buffer medium interface, and drugs dissolved or uniformly dispersed in the polymer are released by zero-order kinetics. A detailed model has been developed that successfully correlates dissolution behavior and various experimental parameters.

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