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Modified release dosage forms offer definite advantages over conventional release formulation of the same drug.The three-layered matrix system overcomes inherent disadvantages of non-linearity associated with the core, covered by two additional layers, each with different rates of swelling, gelling and erosion, is what accounts for the rate of drug release. When the tablet is first swallowed, the drug concentration is high but the surface area is small. As time goes by and the core swells, the surface area expands to compensate for the decrease in drug concentration. Based on these theoretical considerations the three-layered tablets were designed and Diclofenac Sodium, a weakly acidic drug and widely used NSAID, was taken as the model drug to evaluate the comparative release characteristics from different polymer matrices with different amount with the variation in the outer layers as well as in the core.Then the percent release from different batches of Diclofenac Sodium was plotted against time to get the zero order plots. In the zero order plots no true straight lines were obtained but statistically significant differences were found among the release profile.