Hydrophylic matrix tablets containing polyethylene oxides as the retarding polymer has been succesfully employed in the controlled release of drugs. to evaluate the relative influence of drug diffusion and polymer erosion mechanisms in the drug delivery process, we studied the hydration behaviour of metrix tablets containing a water soluble drug and Peos of two different molecularr weigths. the hydration rate, the extent of swelling and the erosion rate of matrices containing the polymer, the drug and tableting exipients, were evaluated in comparison to tablets made of pure polymer. The results of this studies on function of the release behaviour were then discussed. the results show that the higher molecular weight PEO swells to a greater extent and tends to form, upon hydration, a stronger gel, which is therefore less liable to erosion, if compared to the lower molecular weight PEO. Thi difference in the erosion behaviour can explain the different efficiences of the two polymeric products in modulating the delivery rate of the water soluble drug. Moreover, the presence of other soluble components (drug and excipients) in the dosage form enhances the erosion trend of the tablet with a consequent reduction of the efficiency of the polymer in drug release control.
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