In this research, we have reconsidered the current enteric coating techniques and offered a new solution using both theoretical and practical approaches. This approach is based on the fact that salt formation can solubilize the pH-sensitive polymers in water. However, having applied the polymer solution onto the dosage form's surface, the polymer should be converted to the nonionized form for delayed release action. Ammonium hydrogen carbonate (AHC) is used as a buffering agent with dual actions of salting in and desalting the polymer. Following the application of the coating medium onto the dosage form's surface and drying, AHC dissociate completely to ammonia, carbon dioxide, and water converting the polymer to its nonionized form. FT-IR studies on free film samples further confirmed the proposed mechanism. A range of pH-sensitive polymers and other ingredients in water have been successfully applied at the surface of a model ASA tablets, using pan coating technique. According to the SEM observation, the coating layer is very dense and rigid, despite the fact that, the coated amount of the polymers is quit small. The enteric tablets maintain their shapes in acid medium and passed the USP dissolution test for DR ASA tablets.
Copyright 2006 Wiley-Liss, Inc. and the American Pharmacists Association