Emitted dose estimates from Seretide, Diskus and Symbicort Turbuhaler following inhalation by severe asthmatics

The dose emitted from dry powder inhalers may be inhalation flow-dependent. Using an ex vivo method, the Electronic Lung™, we have measured the aerodynamic characteristics of the emitted dose for both active constituents from Seretide® Diskus® (salmeterol xinafoate 50 mcg; fluticasone propionate 500 mcg) and Symbicort® Turbuhaler® (formoterol 6 mcg; budesonide 200 mcg).1 Electronic inhalation profiles were collected from 20 severe asthmatics (mean PEFR 53% predicted) when they inhaled using a placebo Seretide® Diskus® and a placebo Symbicort® Turbuhaler®. These were replayed in the Electronic Lung™ with the respective active inhaler in situ. Mean(S.D.) peak inhalation flow rates (PIFR) through the Diskus® and Turbuhaler® were 94.7(32.9) and 76.8(26.2) l min−1, respectively. From the Electronic Lung™ the Diskus® inhalation profiles provided a mean(S.D.) fine particle dose (FPD) for fluticasone propionate and salmeterol of 20.4(4.8) and 18.4(4.4)% labelled dose. For Turbuhaler® inhalation profiles the FPD was 23.1(12.9) and 20.7(11.1)% labelled dose for budesonide and formoterol, respectively. The linear (p < 0.001) relationships between FPD against PIFR for budesonide and formoterol were 3 (p = 0.002) and 2.8 (p = 0.007) times steeper than fluticasone propionate and salmeterol, respectively. The results highlight a more significant effect of inspiratory flow on variable dosage emission when using the Symbicort® Turbuhaler® compared with the Seretide® Diskus®.