Abstract: The invention relates to an oral pharmaceutical multiple units formulation made up of individual cores containing a pharmacologically active substance, the cores being provided with a coating consisting essentially of a polymer that is insoluble in, impermeable to and non-soluble in water and in gastrointestinal fluids, and a water-soluble pore-creating substance, which is randomly distributed in said polymer, whereby said coated cores form units providing an essential zero order diffusion controlled release rate of said active substance. The invention also comprises a method of preparing these formulations.