The invention relates to a process for preparing a powder formulation for inhalation for use in a dry powder inhaler, said powder formulation comprising: (A) a carrier, comprising : (a) a fraction of coarse particles of a physiologically acceptable carrier having a particle size of at least 60 micron； and optionally (b) a fraction of fine particles comprising a physiologically acceptable excipient, wherein at least 90% of all said fine particles has a volume diameter lower than 15 micron, (B) micronized particles of glycopyrronium bromide, an inhaled corticosteroid (ICS), and optionally a long-acting O2 -agonist (LABA), as active ingredients, wherein said process comprises: (i) preparing by co-milling microparticles consisting of glycopyrronium bromide and a first part of the ICS in a ratio ranging from 80:20 to 70:30 by weight, wherein the volume diameter of said microparticles is not higher than 15 micron； (ii) mixing the carrier, the remaining part of said ICS, and optionally the long-acting O2 -agonist, to obtain a first mixture； and (iii) adding the co-milled microparticles obtained in step (i) to the first mixture obtained in step (ii), to obtain a second, final, mixture.L'invention concerne un procédé de préparation d'une formulation de poudre pour inhalation destinée à être utilisée dans un inhalateur de poudre sèche, ladite formulation de poudre comprenant : (A) un support, comprenant : (a) une fraction de particules grossières d'un support physiologiquement acceptable ayant une taille de particule d'au moins 60 microns ； et facultativement (b) une fraction de particules fines comprenant un excipient physiologiquement acceptable, au moins 90 % de toutes lesdites particules fines ayant un diamètre de volume inférieur à 15 microns, (B) des particules micronisées de bromure de glycopyrronium, un corticostéroïde inhalé (ICS), et éventuellement un agoniste d'O2 à action prolongée (LABA), en tant que principes actifs, ledit procédé comprenant : (i) la préparation
