Preparation and evaluation of microencapsulated and coated ion-exchange resin beads containing theophylline

Anion-exchange resin beads in the theophylline form were prepared and coated with paraffin or encapsulated with ethylcellulose by various methods; one of these products was subsequently coated with paraffin in order to achieve a wide range of release rates and patterns of release. The various products were subjected to rate studies, and it was found that the patterns of release and the rates could be controlled by the cross-linking of the resin and the coating procedures used. A medium and almost constant rate of release was obtained by using ethylcellulose microencapsulation, a coating of hard paraffin, or a combination of both. The amount of coating and the total amount of drug released was also determined.