Effect of formulation and inhaler parameters on the dispersion of spray freeze dried voriconazole particles

Spray freeze drying is a particle engineering technique that allows the production of porous particles of low density with excellent aerosol performance for inhalation. There are a number of operating parameters that can be manipulated in order to optimise the powder properties. In this study, a two-fluid nozzle was used to prepare spray freeze dried formulation of voriconazole, a triazole antifungal agent for the treatment of pulmonary aspergillosis. A full factorial design approach was adopted to explore the effects of drug concentration, atomisation gas flow rate and primary drying temperature. The aerosol performance of the spray freeze dried powder was evaluated using the next generation impactor (NGI) operated with different inhaler devices and flow rates. The results showed that the primary drying temperature played an important role in determining the aerosol properties of the powder. In general, the higher the primary drying temperature, the lower the emitted fraction (EF) and the higher the fine particle fraction (FPF). Formulations that contained the highest voriconazole concentration (80% w/w) and prepared at a high primary drying temperature (-10 °C) exhibited the best aerosol performance under different experimental conditions. The high concentration of the hydrophobic voriconazole reduced surface energy and cohesion, hence better powder dispersibility. The powders produced with higher primary drying temperature had a smaller particle size after dispersion and improved aerosol property, possibly due to the faster sublimation rate in the freeze-drying step that led to the formation of less aggregating or more fragile particles. Moreover, Breezhaler®, which has a low intrinsic resistance, was able to generate the best aerosol performance of the spray freeze dried voriconazole powders in terms of FPF.