The effect of relative humidity on electrostatic charge decay of drugs and excipient used in dry powder inhaler formulation

Electrostatic forces arising from charge accumulation on drug and excipient powders cause agglomeration and adhesion of particles to solid surfaces and problems during the manufacture and use of many pharmaceutical dosage forms, including dry powder inhalers (DPIs). The ability of materials to dissipate the acquired charge is therefore important and the aim of this work was to investigate the charge decay of salbutamol sulfate, ipratropium bromide monohydrate and alpha-lactose monohydrate. Differences in tri-phasic charge decay rates of the three materials in the order ipratropium bromide > lactose > salbutamol sulfate were demonstrated after corona charging and all materials showed an increased decay rate as the relative humidity was increased up to 86%. Preformulation knowledge of charge accumulation and decay in such materials will contribute to formulation, manufacture and performance of pharmaceutical dosage forms in general, and in particular DPIs.