Several parameters were studied for their effect on the dissolution of diclofenac sodium from Voltaren SR and hydroxypropylmethylcellulose (HPMC) based matrix tablets. The results indicate that addition of sodium or potassium chloride to the dissolution medium decreases the solubility of the drug and slows the dissolution rate, with the effect of sodium chloride being greater. The dissolution of the drug was studied in a medium which simulates the changing pH of the pathway followed by the drug as it passes from the stomach to the intestine. Dissolution was found to be inversely related to the rate at which the pH was changed. This may be caused by the deposition of an insoluble drug layer when contact is made with an acid medium. When higher viscosity grades of HPMC are used, slower release rates result. Drug release from Voltaren SR is best described as non-Fickian in an aqueous medium irrespective of whether salt is added; however, a zero-order dependence became evident in pH-changing media. The release of diclofenac sodium from the hydrophilic HPMC matrices follows a non-Fickian transport in all media.
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