Resistivities of placebo and active Diskus® inhalers compared

Objective: Verbal instruction and demonstration of inhalation technique are essential to enhance the effectiveness of inhalation therapy. Placebo devices are commonly used to instruct patients. It is not obvious that patients, who inhale with an adequate flow through an empty placebo Diskus((R)) would also be able to do so with active inhalers containing a strip with powder. The presence of powder may result in a change in resistivity. We compared the resistivities of a placebo Diskus((R)) being empty; a powder filled Diskus((R)) inhaler and a Diskus((R)) inhaler with an empty blister. Methods: A Diskus((R)) inhaler was placed in a box, which enabled measurement or pressure drop and How rates. Ten placebo and ten Ventolin((R)) Diskus((R)) inhalers were measured. Twelve pressure- and flow-profiles were recorded through each device. After each simulated inhalation through a powder filled blister, a second inhalation was performed through the empty blister. The resistivity was calculated by pressure-flow equation. Results: The resistivity of the empty placebo Diskus((R)) inhaler was slightly but significantly higher than both blister filled inhalers, with or without powder (0.0215 vs. 0.0211 and 0.0211 (kPa)(0.5) min (-1))(-1)) (P < 0.001). Conclusion: Patients who are capable of generating sufficient flow through a placebo Diskus((R)) will surely be capable of generating equivalent flows through a Diskus((R)) inhaler containing a strip with active drug substance. (C) 2001 Elsevier Science B.V. All rights reserved.