Dry Powder For Inhalation

A dry powder inhaler, comprising

• a) a multidose powder reservoir containing a dry powder comprising:
• i) a pharmaceutically inactive carrier having particles of noninhalable particle size,
• ii) a pharmaceutically active component comprising at least one finely divided pharmaceutically active compound having particles of inhalable particle size, and
• iii) magnesium stearate as a pulverulent material present in an amount of 0.5 to 5% by weight, based on the total weight of the formulation;
• and
• b) means for delivering metered doses of the pharmaceutically active compound for inhalation,
• wherein said dry powder has a fine particle fraction (FPF) and a fine particle dose (FPD), said powder exhibiting improved stability of FPF and FPD following 4 to 10 days of storage at 40° C. and 75% relative atmospheric humidity compared to a reference lacking magnesium stearate as a pulverulent material.