Effect of maximum inhalation flow and inhaled volume on formoterol drug deposition in-vitro from an Easyhaler® dry powder inhaler

Most patients using dry powder inhalers (DPIs) do not achieve the inhalation parameters recommended for pharmacopoeial in-vitro dose emission testing. The dose emission characteristics of formoterol from an Easyhaler® have been measured using the Andersen Cascade Impactor (ACI) with a maximum inhalation flow (MIF) of 28.3, 60 and 90 L/min and inhaled volumes (Vin) of 240, 750, 1500 and 2000 mL. The total emitted dose (TED) was significantly higher at 90 L/min (p < 0.05), but the difference in the TED between low (28.3 L/min) and high (90 L/min) flow rate was significantly reduced by increasing the Vin. The fine particle dose (FPD) was higher (p < 0.05) at 90 L/min for all Vin values compared to 28.3 and 60 L/min. Similarly the mass median aerodynamic diameter (MMAD) was smaller at 90 L/min across all Vin values. Dose emission characteristics were lower at 240 mL for both MIFs. The results for 240 mL could be due to an insufficient Vin pulled through the ACI or incomplete emptying of the dose metering cup. This study shows that the FPD, %FPF and MMAD were not significantly affected by the vin ≥ 750 mL and that an inhaled volume as low as 750 mL could be used with the ACI.