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Abstract
The objective of this work was to investigate the effect of thermal treating on the release rate of diclofenac sodium from Eudragit RS and Eudragit RL matrices. Eudragit RS and RL are nonswelling polymers that have a low glass transition (Tg) temperature. The matrices were thermally treated at different temperatures (40, 50, 60, and 70°C) for different periods of times (2, 5, and 24 h). The results showed that thermal treating at temperatures less than the Tg of the polymer has no effect on the release of the drug, whereas heat-treating at temperatures higher than the Tg decreases the release rate of diclofenac sodium from matrices. It was shown that the duration of heat treatment was also an important factor in controlling the release rate of diclofenac sodium from Eudragit matrices. The results showed that an increase in the duration of heat treatment from 2 h to 24 h resulted in a reduction in the release rate of the drug. Scanning electron microscopy of the cross section of the tablet before and after heat treating showed that the tablets were deformed and fused into a continuous and homogeneous structure after heat treating. Thermally treated tablets demonstrated fewer surface defects than did nonthermally treated tablets. These structural changes in the tablet compacts resulted in a matrix structure that decreased the release rate of the diclofenac sodium from Eudragit matrices.