The effect of water on matrix formation in sustained release tablets containing poly(ethyl acrylate, methyl methacrylate)

The effect of water on the behavior of poly(ethyl acrylate, methyl methacrylate) 2:1 [poly(EA-MMA)] matrix systems was studied in tablets containing diclofenac sodium (DS) as a model drug. DS:poly(EA-MMA) granules were either untreated, or treated at 50 °C for 5 h, or treated at 50 °C for 5 h and sprayed with water. Half of the tablets produced from these granules were thermally treated at 50 °C for 1 h. Increased water content minimized differences between the tablets with low polymer content and reduced their release rate to match the slower release from tablets with high polymer levels. Furthermore, increased water content in thermally treated granules resulted in formation of a soft matrix, with lower strength and stiffness. Based on the results and well-known plasticizing effect of water, it appears that complex mechanisms of matrix formation rely on the transition of the polymer meshwork from glassy to rubbery state.