In the first variant, the pharmaceutical composition comprises antibiotic and prebiotic in the form of oligosaccharide of a group comprising fructooligosaccharides, galactooligosaccharides, maltooligosaccharides and isomaltooligosaccharides the polymerisation degree of which ranges from 2 to 10, the particle size is equal to less than 0.3 mm and the purity is of at least 95%, wherein the antibiotic particle size ranges from 20 to 200 mkm and the antibiotic and oligosaccharide are contained with a mass ratio ranging from 1:1 to 1:100 respectively. In the second variant, the pharmaceutical composition comprises antibiotic which is in the form of a powder with the particle size ranging from 20 t0 200 mkm and is selected form a group consisting of beta-lactams, including the combination thereof with bacterial betalactamase inhibitors, azalides, fluoroquinalones, amphenicols, glycopeptides, ansamycins, nitrofurans, phosphonic acid derivatives, cycloserine and trimetoprim. The prebiotic is in the form of a powder oligosaccharide, the polymerisation degree of which ranges from 2 to 10, the particle size is equal to less than 0.3 mm and the purity is of at least 95%, wherein the antibiotic and oligosaccharide are contained with a mass ratio ranging from 1:1 to 1:100 respectively. The above-mentioned compositions are used for preventing intestinal dysbiosis during antibiotic therapy and are perorally administered. The inventive composition produces a stimulating effect on intestinal lactobacilli and bifidobacteria simultaneously inhibiting the growth and proliferation of extraneous or pathogenic microflora.antibiotique et un prébiotique, qui est un polysaccharide du groupe contenant des fructo-oligosides, galacto-oligosides, xylo-oligosides, malto-oligosides ou iso-malto-oligosides, avec un degré de polymérisation de 2 à 10, une taille de particules jusqu’à 0,3 mm, et une pureté égale ou supérieure à 95% l’antibiotique possède une taille de particules de 20 à 200 micromètres
