Use of ion-exchange resins to prepare 100 microm-sized microcapsules with prolonged drug-release by the Wurster process.

Ion-exchange resin (IER)--drug complexes were used as core materials to explore their capability to prepare a 100 microm-sized, highly drug-incorporated microcapsule with a prolonged drug release by the Wurster process. Diclofenac sodium was loaded into Dowex 1-X2 fractionated into 200--400 mesh and subsequently microencapsulated with two types of aqueous colloidal polymer dispersion, Aquacoator Eudragit RS30D. The mass median diameter and drug content of the microcapsules thus obtained were 98 microm and 46% with Aquacoat, and 95 microm and 50% with Eudragit RS30D, respectively. Each microcapsule was obtained at a product yield of 94%. The rate of drug release from the microcapsules was highly dependent on the encapsulating materials. For the microcapsules coated with Aquacoat, diclofenac sodium was found to be rapidly released over 4 h, even at a 25 wt% coating level because of cracks on the microcapsule surfaces resulting from the swelling stress of the drug-loaded IER cores. In contrast, significantly prolonged drug-release was achieved in the microcapsules prepared with Eudragit RS30D: even such a very low coating level as 3 wt% provided an exceptionally prolonged drug-release over 24 h. The results indicated that the use of IER along with a flexible coating material would be a feasible way to prepare a prolonged release type of microcapsules with a diameter of 100 microm and a drug content of more than 50% by the Wurster process.