Abstract

The aim of the present study was to explore the potential effect of the coating material
on the aerodynamic particle size distribution (APSD) of formoterol from Oxis
Turbohaler®

using mixing inlet with Andersen Cascade Impactor (ACI) operated at
flow rate of 60 Lmin-1. As the aerodynamic properties of the emitted dose from a dry
powder inhaler (DPI) are usually flows dependent but have not been calibrated for
low flow rates at yet. We have used novel methodology to measure these at even low
flow of 28.3 Lmin-1. The Andersen Cascade Impactor (ACI) designed for 60 Lmin-1
was adapted to include a mixing inlet (MIXINLET) which allows inhalation flows
through the DPI from 5 to 60 Lmin-1. The mean (SD) Mass Median Aerodynamic
Diameter (MMAD) for no coating, silicone, 100% and 50% glycerin, 100% and 50%
propylene glycol was 2.17 ± (0.06), 1.40 ± (1.23), 2.00 ± (0.42), 2.10 ± (0.10), 3.20 ±
(0.00) and 3.17 ± (0.06) μm respectively. The geometric standard deviation (GSD)
values for no coating, silicone, 100% and 50% glycerin, 100% and 50% PEG were
1.70, 0.90, 2.30, 2.53, 1.80 and 1.83 respectively. The mean ± (SD) fine particle dose
(FPD) for no coating, silicone, 100% and 50% glycerin, 100% and 50% PPG was
32.31 ± (8.19), 21.69 ± (18.83), 21.13 ± (0.06), 3.86 ± (0.10) and 2.55 ± (0.05)
respectively. The one way ANOVA with the application of Bonferroni’s correction
was used to compare the aerodynamic droplet characteristics of the formoterol. The
results indicate a significant difference between aerodynamic PSD when different
coating materials were used. The MMAD was highest for PPG making it a suitable
coating agent compared to other coating materials.