A process for preparing a powder formulation for inhalation for use in a dry powder inhaler, said powder formulation comprising: a carrier, comprising: (a) a fraction of coarse particles of a physiologically acceptable carrier having a mean particle size of at least 175 μm; and (b) a fraction of fine particles, consisting of a mixture of 90 to 99.5 percent by weight of particles of a physiologically acceptable excipient and 0.5 to 10 percent by weight of a salt of a fatty acid, wherein at least 90% of all said fine particles have a volume diameter lower than 15 microns, wherein the weight ratio of said fine particles to said coarse particles is 5:95 to 30:70; and micronized particles of an antimuscarinic drug, a long-acting β 2 -agonist (LABA) and, optionally, an inhaled corticosteroid, as active ingredients, wherein said process comprises: (i) mixing said carrier, said long-acting β 2 -agonist, and, optionally, said inhaled corticosteroid in a vessel of a shaker mixer at a speed of rotation not lower than 16 r.p.m. for a time of not less than 60 minutes, to obtain a first mixture; and (ii) adding said anti-muscarinic drug to said first mixture, to obtain a second mixture, and mixing said second mixture at a speed of rotation not higher than 16 r.p.m. for a time of not more than 40 minutes, wherein the long-acting β 2 -agonist is selected from the group consisting of formoterol, salmeterol, indacaterol, olodaterol, and vilanterol; the anti-muscarinic drug is selected from the group consisting of glycopyrronium bromide or chloride, tiotropium bromide, umeclidinium bromide, and aclidinium bromide; the inhaled corticosteroid is selected from the group consisting of beclometasone dipropionate and its monohydrate form, budesonide, fluticasone propionate, fluticasone furoate, and mometasone furoate. a carrier, comprising: (a) a fraction of coarse particles of a physiologically acceptable carrier having a mean particle size of at least 175 μm; and (b) a fraction of fine particles, consisting of a mixture of 90 to 99.5 percent by weight of particles of a physiologically acceptable excipient and 0.5 to 10 percent by weight of a salt of a fatty acid, wherein at least 90% of all said fine particles have a volume diameter lower than 15 microns, wherein the weight ratio of said fine particles to said coarse particles is 5:95 to 30:70; and (a) a fraction of coarse particles of a physiologically acceptable carrier having a mean particle size of at least 175 μm; and (b) a fraction of fine particles, consisting of a mixture of 90 to 99.5 percent by weight of particles of a physiologically acceptable excipient and 0.5 to 10 percent by weight of a salt of a fatty acid, wherein at least 90% of all said fine particles have a volume diameter lower than 15 microns, micronized particles of an antimuscarinic drug, a long-acting β 2 -agonist (LABA) and, optionally, an inhaled corticosteroid, as active ingredients, wherein said process comprises: (i) mixing said carrier, said long-acting β 2 -agonist, and, optionally, said inhaled corticosteroid in a vessel of a shaker mixer at a speed of rotation not lower than 16 r.p.m. for a time of not less than 60 minutes, to obtain a first mixture; and (ii) adding said anti-muscarinic drug to said first mixture, to obtain a second mixture, and mixing said second mixture at a speed of rotation not higher than 16 r.p.m. for a time of not more than 40 minutes, (i) mixing said carrier, said long-acting β 2 -agonist, and, optionally, said inhaled corticosteroid in a vessel of a shaker mixer at a speed of rotation not lower than 16 r.p.m. for a time of not less than 60 minutes, to obtain a first mixture; and (ii) adding said anti-muscarinic drug to said first mixture, to obtain a second mixture, and mixing said second mixture at a speed of rotation not higher than 16 r.p.m. for a time of not more than 40 minutes,