The effect of inhalation flow on the performance of a dry powder inhalation system.

Dry powder inhalation systems are composed of a small amount of active ingredients and a larger amount of filler. The drug particles are believed to be bound by the filler crystals. The complexes are too large to be inhaled and need to be separated before they enter the lungs. This is done by the air patients inhale through the inhaler. Asthmatics can show low inhalation flows and the performance of a dry powder inhaler at low flows was investigated. It was shown, that small particles (less than 5 microns) separate swiftly at low flows and larger particles (greater than 5 microns) will need higher flows. The conclusion is that dry powder inhalation preparation do not show a simple separation pattern.