Background: The emitted dose (ED) from most dry powder inhalers (DPIs) is almost independent of peak inspiratory flow (PIF) above a certain value, which is specific to the individual DPI. However, the ED of the Turbuhaler® (TBH) increases linearly with PIF increments. This study investigated the powder clearance and clinical utility of TBH performance features by using the photo-reflection method (PRM), a type of laser photometry. Methods: Pulmicort® (PLM) (containing budesonide only) and Symbicort® (SMB) (drugs with lactose particles) were inspired with a ramp-up pattern of several PIF intensities using a vacuum pump. Time trajectories of particle release and PIF were then compared. Results: The particle-release trajectories from both types of DPIs were similar, consisting of a sharp increment phase (∼0.15 seconds) followed by exponential decay. Both onset to the peak of particle-release time and particle-release times were not affected by PIF changes when the PIF was >40 L/min. EDs from both TBHs were linearly related to PIFs, and the slope of the regression equation for SMB was 2.4-fold larger than that of PLM. The peak of the released particles (PKIED) was also linearly related to PIF. A linear relationship was also observed between ED and PKIED in both TBHs, and these regression lines overlapped. Conclusion: EDs from the TBH were dependent on PKIED. Therefore, rapid, initially strong, and deep inhalation should be advised while using the TBH. PRM could measure the fine and small amount of particles released from the TBH.
Keywords: inhaled flow pattern; laser photometry; particle release.