FORMATION OF WATER-INSOLUBLE GEL IN DRY-COATED TABLETS FOR THE CONTROLLED-RELEASE OF THEOPHYLLINE

Sodium alginate (ALNa) of a natural polysaccharide is known to form a water-insoluble gel when combined with a bivalent metal, In this study , we prepared tablets containing ALNa and calcium gluconate (GLCa) as a bivalent metal, and studied the application of the water-insoluble g el involving the controlled release of a test drug by permeation of wa ter. Dry-coated tablets containing theophylline (TP) as a model drug, ALNa and GLCa were prepared by the dry ponder compression method. The controlled release of TP was evaluated by the dissolution test accordi ng to JP XIII. The release rate was extremely high far the tablets whi ch contained only TP and GLCa. A zero order or sigmoidal release profi le was observed for the tablets that contained only TP and ALNa. On th e other hand, the lowest dissolution rate and a sigmoidal release prof ile were observed for the tablet containing TP and GLCa in its core an d ALNa in its outer phase, These results suggest that dry-coated table ts containing ALNa and GLCa and prepared by the direct powder compress ion method would be useful for the controlled release of drugs.