Release mechanisms of theophylline from newly designed sustained release granules and tablet which contains sustained release granules have been studied by dissolution tests and observation of scanning electron photomicrographs. Sustained release granules have been prepared from plain granules by coating with water-insoluble materials. Dissolution profiles showed that approximately 90% of the drug was released in 8 h from granules and tablet, indicating that both preparations prolonged release of the drug. By comparison of several release kinetic theories, it was suggested that the release rate of the drug from these preparations was mainly dependent on the rate of drug diffusion through the membrane. The mean cumulative absorption profile after administration of sustained release granules to four healthy volunteers was very similar to the release profiles from the granules. Therefore it may be expected that absorption of the drug was affected slightly by ingestion of food and changes in gastrointestinal motility, gastric emptying rate and pH in the gastrointestinal tract.
