Pharmaceutical formulations for dry powder inhalers comprising a low-dosage strength active ingredient

The invention provides a formulation to be administered as dry powder for inhalation suitable for efficacious delivery of low-dosage strength active ingredients to the low respiratory tract of patient. In particular, the invention provides a formulation comprising microparticles constituted of microparticles of a low-dosage strength active ingredient and microparticles of an excipient wherein the MMD of the microparticles is comprised between 2 and 15 micron, at least 10% of the microparticles has a mass diameter (MD) higher than 0.5 micron, and the process of preparation thereof.