Effect of Relative Humidity on Bipolar Electrostatic Charge Profiles of dry Powder Aerosols

This work investigated the effect of relative humidity (RH) on bipolar electrostatic charge profiles of dry powder inhaler aerosols using the Bipolar Charge Analyzer (BOLAR).

Two commercial products, Pulmicort® (400 μg, budesonide) and Bricanyl® (500 μg, terbutaline sulfate) Turbuhaler®, were used as model dry powder inhalers (DPIs) in this study. Three individual doses from each Turbuhaler® were sampled at 15, 40, 65 and 90% RH. Subsequently, charge and mass profiles were determined for each dispersion.

The aerosols from these two Turbuhaler® DPI were bipolarly charged, with larger particles carrying negative charge and smaller particles positive charge. Particles changed polarity around 2.60-4.17 μm and 0.95-2.60 μm for Pulmicort® and Bricanyl®, respectively. The effect of RH on particles differed between DPIs even though the mass output was not significantly affected. The net charge profiles of Pulmicort® were relatively independent of RH, whereas those of Bricanyl® showed a reduction in the charge magnitude with increasing RH. Both positive and negative charge profiles followed a similar trend with the change in RH and individually they had higher magnitudes than the measured net charge.

This study showed drug-specific bipolar charging of the Turbuhaler® DPI aerosols at varied RHs. Bricanyl® was more susceptible to RH and showed decreased bipolar and net charge levels with increasing RH, in comparison to Pulmicort®.