A Novel Technique to Assess Drug Substance Particle Size in a Complex Inhaled Formulation

Dry powder inhalers, comprising an active pharmaceutical ingredient (API) and carrier excipients, are often used in the delivery of pulmonary drugs. The stability of the API particle size within a formulation blend is a critical attribute for aerodynamic performance but can be challenging to measure. The presence of excipients, typically at concentrations much higher than API, makes measurement by laser diffraction very difficult. This work introduces a novel laser diffraction approach that takes advantage of solubility differences between the API and excipients. The method allows insight into the understanding of drug loading effects on API particle stability of the drug product. Lower drug load formulations show better particle size stability compared with high drug load formulations, likely due to reduced cohesive interactions.