Inhalation characteristics and their effects on in vitro drug delivery from dry powder inhalers .3. The effect of flow increase rate (FIR) on the in vitro drug release from the Pulmicort 200 Turbuhaler

The efficacy of dry powder inhalers (DPIs) is usually related to peak inspiratory flow rate (PIFR) through the device. In this study, the effect of the acceleration in flow rate (flow increase rate: FIR) on the fine particle output from the Pulmicort 200 Turbuhaler is discussed. Inspiratory flow curves of 11 healthy volunteers were recorded during 'calm but deep' and 'fast and deep' inhalation, respectively, both as a function of air flow resistance. Thereby, attained FIRs were calculated for the section of the flow curve between 20 and 30 1/min (FIR20-30). Mean values for an air flow resistance similar to that of the Turbuhaler were approximately 2 1/s(2) during calm but deep and 10 1/s(2) during fast and deep inhalation. In vitro fine particle output from the Turbuhaler was studied with a four stage cascade impactor. This output increased between 1 and 5 1/s(2) but appeared to be constant at higher FIR20-30-values. The output was also found to be independent of PIFR when compared at the same FIR20-30. Maximum output could therefore already be obtained at 40 1/min for FIR20-30 greater than 5 1/s(2), which could easily be achieved by the healthy volunteers. (C) 1997 Elsevier Science B.V.