Effect of the molecular size of carboxymethylcellulose and some polymers on the sustained release of theophylline from a hydrophilic matrix.

The objective of this study was to investigate the influence of the molecular size of carboxymethylcellulose (cmc) and some hydrophobic polymer additives on the release properties of theophylline from tablet matrices. The cmc matrices were prepared by the conventional wet granulation method. The granules were evaluated for angles of repose, bulk density, compressibility index, and porosity, while the tablets were subjected to hardness, friability and compression tests. All tablet formulations showed acceptable pharmacotechnical properties. Low molecular size cmc (cmc-L) showed the shortest drug release t50% of 27 min, for medium size cmc (cmc-M) it was 55 min and for high molecular size cmc (cmc-H) 200 min. In general, the results showed that the drug release rate decreases with an increase in the molecular size of cmc. All polymer additives, ethylcellulose, cellulose acetate phthalate and Eudragit 1-100 retarded theophylline release from cmc-L and cmc-H, with ethylcellulose having the most pronounced effect on cmc-L. Kinetic studies using Hixson-Crowell and Peppas-Ritger equations showed that different drug release mechanisms were involved in controlling drug dissolution from the tablets. The drug release mechanism was influenced by both the molecular size of cmc and the presence of polymer additives.