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

PURPOSE: 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).

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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®.