Dry powder inhalers have become a popular inhalation delivery system due to good drug stability and a minimal need for patient coordination.[1] Given that the efficacy of the drug is dependent on where the dose is delivered, it is important to understand the physicochemical properties of the aerosol to predict dose. Once inhaled, the dry particles experience a warm humid environment where, depending on their solubility properties, they can take up water. A particle that fully dissolves in the aerosol phase will grow during inhalation, the magnitude of growth is controlled by its hygroscopicity. This dynamic size change influences the deposition mechanism, thus the deposited fraction.

Here, we report primary dissolution measurements in the aerosol phase of varying systems; pharmaceutical aerosol, salt compounds and sugar compounds. An adapted comparative kinetics electrodynamic balance (CK-EDB) has been used to replicate the dissolution process of dried particles in the lung. The CK-EDB traps individual particles within its core and monitors size/phase change as a function of time (0.01 second resolution) and relative humidity, which can be switched in less than one second. It accurately replicates the dynamic size change of aerosolised drug mixtures during generation and inhalation.