The present invention relates to aggregate particles comprising nanoparticulate drug particles. In particular, the present invention is directed to aggregate particles comprising nanoparticulate drug particles of umeclidinium bromide and optionally vilanterol trifenatate and/or fluticasone furoate. Aggregate particles of the present invention may further comprise nanoparticulate excipient particles and one or more binders. The invention also relates to powder compositions suitable for inhalation that comprise said aggregate particles, processes of producing said aggregate particles, and use of said powder compositions in the treatment of respiratory diseases, such as asthma and COPD.