An anti-acid pharmaceutical composition for the rapid and prolonged neutralization of gastric acidity with mucosa-protecting activity in powder form to prepare, by dispersion in water, a pharmaceutical solution or suspension for oral use characterized in that the composition includes sodium alginate; an anti-acid soluble agent or a combination of anti-acids; an inhibitor of proton pump; diluent and sweetening agents, wherein a) at least 30% of sodium alginate present in the formulation along with the total of the inhibitor of proton pump are homogeneously distributed over the surface of the total soluble anti-acid agent of the combination of anti-acids of the composition; and b) the rest, about 70%, of sodium alginate present in the formulation contains a percentage of humidity of less than 2%.