Cascade impactor analysis

The in vitro aerodynamic assessment of the three DPI products was carried out using a next generation impactor, NGI (Copley Scientific Ltd) equipped with a pre-separator and a micro orifice collector (MOC), following the procedure detailed in the European and US Pharmacopoeia.^(10,11) The NGI was connected to a HCP5 vacuum pump (Copley Scientific Ltd). For each single experiment, three doses were discharged into the NGI at 30, 40, 60, and 90 L/min for a duration of time such as to obtain an air passing volume of 4 L. The details of the experimental plan performed are illustrated in Table 1. This protocol was applied to two distinct devices for each inhaler in order to take into account possible intra-batch variability (NEXThaler batch #{"type":"entrez-nucleotide","attrs":{"text":"B10814","term_id":"2091935","term_text":"B10814"}}B10814, Diskus batch #3983A, and Symbicort batch #NF3942).

Experimental Plan of Doses Collected Inside the NGI for Each of the Two Devices Discharged

The required flow rate was obtained by adjusting the critical flow valve, ensuring that critical flow conditions were always maintained (flow meter DFM2000 and Critical Flow Controller Model TPK, Copley Scientific Ltd). NGI stages were coated with Tween 20/ethanol, 2% w/v solution, in order to prevent particle bouncing inside the impactor. After the required actuations were performed into the NGI, the powder deposited on the different portions of the impactor was collected using a 40:60 (v/v) water:methanol mixture, filtered (PTFE 0.45 μm, Sartorius AG, Goettingen, Germany) and then, drugs quantified by HPLC.

Fine particle masses and fractions <5 μm of drugs released by Foster^® NEXThaler were also assessed using inhalation volumes of 2.0 and 4.0 L, adjusting the flow rate through the inhaler at 55 L/min±5% to provide a 4.0 kPa pressure drop across the device (flow meter DFM2000 and Critical Flow Controller Model TPK, Copley Scientific Ltd). As a consequence, the aspiration time was set at 2.18 or 4.36 s, respectively. Three doses were actuated into either NGI or Andersen Cascade Impactor, ACI (Copley Scientific Ltd) for each experiment and the test was performed in triplicate.

Fine particle mass lower than 5 μm (FPM<5 μm), extrafine particle mass lower than 2 μm (EFPM<2 μm), fine particle fraction (FPF%), mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) were determined from the analysis of the NGI/ACI data. The calculation of the aerodynamic parameters was performed by using CITDAS (Copley Inhaler Data Analysis Software, UK).

MMAD and GSD were calculated based upon the inverse normal of the cumulative percentage under the stated aerodynamic diameter versus the log of the effective cut-off diameter. Linear regression of the five data points closest to 50% of the cumulative particle mass that entered the impactor was performed to compute the MMAD and GSD. The cut-off diameter of NGI stages was calculated and corrected for the different flow rates according to USP. In all impactor tests conducted, the mass balance was within±15% of the labelled dose.