Abstract: This invention relates to oral pharmaceutical preparations that comprise a pharmacologically active drug bound to small particles of an ion-exchange resin. Drug-resin complexes are coated with an aqueous based diffusion barrier comprising a water-permeable, film forming polymer that is relatively insoluble in gastrointestinal fluids thereby providing a controllable sustained release of drug under conditions encountered in the gastrointestinal tract. At least some of the barrier coated drug-resin particles may be coated with an enteric coating to provide a tailored release profile.