Spray Dried Formulations for Inhalation—Meaningful Characterisation of Powder Properties

Spray drying as a particle engineering technique is of increasing interest in the field of inhalation and is already being utilised e.g., for the PulmoSphere(TM) products. As spray dried particles tend to agglomerate and are mechanically instable, low dose filling processes can be difficult. This study correlates powder flowability tests of spray dried formulations with filling processes with drum and dosator systems. Four pulmonary and four nasal powders with different characteristics in terms of shape, composition, and surface polarity were prepared and characterised for powder flowability according to Ph. Eur. and by powder rheometry. All formulations were filled with a manual drum TT and a dosator system. The classical flowability tests according to the Ph. Eur. showed a bad flow behaviour for hydrophilic pulmonary powders (x(50) ~ 3 µm), whereas hydrophobic pulmonary particles and nasal particles (x(50) ~ 25 µm) showed a better flowing behaviour. Powder rheometry supports this finding but can better differentiate flow behaviours.