Formulation of Biopharmaceutical Dry Powder Inhaler Using the Void Forming Index (VFI) to Detect and Avoid Powder Caking in Dry Powder Inhaler Formulations

It is mandatory to detect the powder cohesiveness of biopharmaceutical dry powder inhaler (Bio-DPI) formulations and their effect on their performance. Normally, Bio-DPI formulations consist of highly cohesive components with higher drug amounts than small molecules. Herein, a formulation study of a high-drug-ratio Bio-DPI was performed, detecting the risk of powder caking in DPI formulations. The Bio-DPI formulation was manufactured via the spray-dry method followed by mixing with excipients. Powder caking was detected through the void forming index (VFI), which was calculated using pressure drop measured by inverse gas chromatography (iGC). Since VFI can be used to evaluate the structural changes induced by powder caking over time with less than 1 g of sample, VFI is considered suitalbe to apply for DPI formulation screening. The risk of powder caking was detected in spray dryed particles at more than 45% relative humidity (RH) humidity condition, mannitol (as a carrier particle) and magnesium stearate (as a lubricant) were added to the formulations. With formulation screening, addition of more than 40% of mannitol was suggested to reduce the risk of powder caking. Selected DPI formulation remained higher emitted ratio (95.6%), than spray dried particle (52.5%) at 25 °C 65% RH condition for 1-month storage. In conclusion, VFI measurement is useful for selecting the DPI formulation by mitigating powder caking risk with limited samples.