Controlled release bead, pharmaceutical formulation comprising the same and production thereof

A controlled release bead comprises: (i) a core unit of a substantially water-soluble or water-swellable inert material; (ii) a first layer on the core unit of a substantially water-insoluble polymer; (iii) a second layer covering the first layer and containing an active ingredient; and (iv) a third layer of polymer on the second layer effective for controlled release of the active ingredient, wherein the first layer is adapted to control water penetration into the core. A method of producing the controlled release bead is also disclosed.