In vitro testing of two formoterol dry powder inhalers at different flow rates.

The efficiency of two different dry powder inhaler systems for the application of the beta2-sympathomimetic drug Formoterol in the lungs has been tested in vitro. Particle size distributions for each device have been measured at four different flow rates (28.3, 40, 60, and 80 L/min) using an Andersen-Impactor. Mass median aerodynamic diameters (MMAD) of the dispersed powder and deposition of the drug in the respiratory tract was determined using a semiempirical lung deposition model. The optimum output for both devices determined by in vitro measurements is supposed to be achieved with flow rates of 40-60 L/min. The Oxis Turbuhaler delivers the smaller particles as the Foradil P Aerolizer and, thus, the Formoterol deeper into the lungs, but the high specific airflow resistance will influence the ability of patients with severe asthma and children to use the system.