Abstract: The invention relates to a new pharmaceutical preparation of high acid-binding capacity, of delayed effect, of increased bioavailability for neutralization of gastric acid and optionally to other pharmaceutical preparations acting in the gastrointestinal tract, first of all of laxative effect by mixing 100 parts by mass of a powdered basic magnesium compound or the powdered mixture of basic magnesium compounds and basic aluminium compounds with 2-2500 parts of a dry or swollen organic acid of polymeric character and therapeutically acceptable, e.g. cellulose-glycolic acid, starch-glycolic acid or polymer acrylic and/or methacrylic acid, letting this powdered mixture to stand for 1-24 hours at the temperature of 20.degree.-80.degree. C.