Properties of hot-melt extruded theophylline tablets containing poly(vinylacetate)

The objectives of this study were to investigate the properties of poly(vin yl acetate) (PVAc) as a retardant polymer and to study the drug release mec hanism of theophylline from matrix tablets prepared by hot-melt extrusion. A physical mixture of drug, polymer, and drug release modifiers was fed int o the equipment and heated inside the barrel of the extruder. The cylindric al extrudates were either cut into tablets or ground into granules and comp ressed with other excipients into tablets. Due to the low glass transition temperature of the PVAc, the melt extrusion process was conducted at approx imately 70 degrees C. Theophylline was used as the model drug in this study . Theophylline was present in the extrudate in its crystalline form and was released from the tablets by diffusion. The Higuchi diffusion model and pe rcolation theories were applied to the dissolution data to explain the drug release properties of the matrix systems. The release rate was shown to be dependent on the granule size, drug particle size, and drug loading in the tablets. Water-soluble polymers were demonstrated to be efficient release rate modifiers for this system.