title: Formulation parameters affecting the preparation and properties of microencapsulated ion-exchange resins containing theophylline.
abstract: A method of microencapsulating theophylline ion-exchange resins with ethylcellulose was developed to produce smooth and uniform coats which were predominantly mononucleated. This was achieved by controlling the amount of ethylcellulose and the particle size, and through the use of a protective colloid, polyisobutylene. The rate of release of theophylline was influenced by the ion-exchange resin crosslinking, the amount of ethylcellulose, and the smoothness of the coat. Mesh size and polyisobutylene did not appear to affect the rate in a regular manner. It was found that the release rate from coated resins with low crosslinking followed a logarithmic plot, indicating membrane-controlled release, whereas coated resins with high crosslinking fitted a t1/2 plot, suggesting particle diffusion control.
authors.affiliation: Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: M G
authors.initials: MG
authors.lastname: Moldenhauer
authors.forename: J G
authors.initials: JG
authors.lastname: Nairn
mesh_terms: D002214:Capsules; D002482:Cellulose / Q000031:analogs & derivatives; D003692:Delayed-Action Preparations; D004058:Diffusion; D004339:Drug Compounding; D007475:Ion Exchange Resins; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D013806:Theophylline / Q000008:administration & dosage*
chemical_list: D002214:Capsules; D003692:Delayed-Action Preparations; D007475:Ion Exchange Resins; C013517:ethyl cellulose; D002482:Cellulose; D013806:Theophylline