The effect of flow rate on drug delivery from the Pulvinal, a high-resistance dry powder inhaler.

Dry powder inhalers vary widely in their resistance to flow. When the resistance is high, airway resistance can be neglected and inspiration rates will be determined primarily by the device. Provided that the patient can generate adequate flow rates to aerosolize the dose, variability of emitted dose and fine particle dose should be reduced. For in vitro simulation, these concepts are explored using a Pulvinal device. In conditions likely to be encountered in patient use, the emitted dose showed little dependence (80-102 micrograms) as the flow rate increased from 28 to 63 L/min. The fine particle dose was more sensitive, increasing by a factor of 1.6 from 22 to 35 micrograms. These variations are less than those observed with the Turbohaler, a device of intermediate resistance and very much lower than those observed with the Rotahaler, a low-resistance device.