Particle engineering by spray drying is an interesting alternative to the widely used interactive mixtures for DPI as powder properties can be specifically tailored. As the materials are typically of low density and exhibit a large surface due to their small particle size, resulting in poor flowability, difficulties in the filling process can occur. In this study the fillability of spray dried powders with different particle shape and surface polarity was tested with a vacuum drum system and a dosator system. A design of experiment was issued to investigate the factors influencing the filling process with the drum system. Furthermore, the impact of the filling process on the emitted dose (ED) for the Twister® and Cyclohaler® was evaluated. A possibly lower ED was expected, because of the built up and poor dispersing plugs resulting from the filling process. Easy flowing powders (ffc > 4) could be filled with the drum system. It was found, that the influence of the vacuum, leading to higher fill weights, if applied stronger, was significant (p < 0.05). Powders with an ffc < 4 could not be filled with the drum system but with the dosator system. There, the height of the powder bed determines the fill weight. There was no effect of the dosator filling process seen on the emitted dose from both inhalers. The results for the design of experiment evaluating the effect of the drum filling system on the ED showed no significant or a not relevant influence.
This study showed even spray dried powders for inhalation with their low mechanical stability can be filled with suitable equipment, based on their flowability. The formed plugs could still be well dispersed, so no negative impact on the emitted dose could be seen compared to spatula-filled capsules with no administered compression.