The relationship between inspiratory pressure and flow through dry powder inhaler available in Japan

OBJECTIVE: Recently many of the inhaled drugs are provided as dry powder formula and prescribed for such diseases as COPD and asthma exacerbation. Inspiratory flow rate through the dry powder device (DPI) has a significant influence on therapeutic response in these disease conditions. We planned to measure flow vs. pressure relationships of almost all of the DPIs available in Japan. METHODS: Driving pressure (PI) and flow through the DPI were measured and the linear regression lines between PI and flow(2) were drawn. RESULTS: The slope and intercept of the regression lines were as follows: Turbuhaler for Pulmicort 79.26 (l/s)(2)/cmH2O, 626 (l/s)(2), Turbuhaler for Symbicort 88.99, 688, Twisthaler 56.37, 478, Diskus 125.98, 872, Diskhaler, 166.98, 780, Handihaler, 54.88, 498, Clickhaler, 78.37, 452. We drew P(I) vs flow curves of each DPIs for instruction of DPI devices to the patients. CONCLUSION: Inspiratory pressure is an excellent parameter to indicate optimal flow through DPI. Early escalation of medication may be important in the patients using Turbuhaler or Twisthaler that has higher resistance in inspiratory channel.