Effect of Relative Humidity on the Electrostatic Charge Properties of Dry Powder Inhaler Aerosols

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Abstract
At present, there is no published data examining the effect of relative humidity on the electrostatic charges of dry powder inhaler aerosols. The charging behaviour of two commercial products, Pulmicort® and Bricanyl® Turbuhalers®, were investigated using an electrical low pressure impactor (ELPI). ELPI was successfully modified to disperse the aerosols at 60 l/min. Four doses from each new inhaler were sampled at 15, 40, 65, and 90% RH. Particles deposited on the impactor stages according to their aerodynamic diameters and their charges were measured simultaneously by the electrometers. The drug in each size fraction was quantified using HPLC. Both products generated bipolar charges. The charging behaviour of the two types of inhaler showed different humidity dependence although the mass output was not significantly affected. The absolute specific charge of budesonide fine particles from Pulmicort® was the lowest at 40% RH but increased at lower and higher RHs. In contrast, the terbutaline sulfate fine particles from Bricanyl® followed the expected trend of charge reduction with increasing RH. The distinct trends of charging of aerosols from Pulmicort® and Bricanyl® Turbuhalers® was explained by differences in hygroscopicity and other physicochemical factors between the two drugs.

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