Large porous particles for respiratory drug delivery. Glycine-based formulations
Large porous particles are becoming increasingly popular as carriers for pulmonary drug delivery with both local and systemic applications. These particles have high geometric diameters (5–30 μm) but low bulk density (˜ 0.1 g/cm3 or less) such that the aerodynamic diameter remains low (1–5 μm). In this study salbutamol and budesonide serve as model inhalable drugs with poor water solubility. A novel method is proposed for the production of dry powder inhaler formulations with enhanced aerosol performance (e.g. for salbutamol-glycine formulation the fine particle fraction (FPF ≤ 4.7 μm) value is 67.0 ± 1.3%) from substances that are poorly soluble in water. To overcome the problems related to extremely poor aqueous solubility of the APIs, not individual solvents are used for spray freeze-drying of API solutions, but organic-water mixtures, which can form clathrate hydrates at low temperatures and release APIs or their complexes as fine powders, which form large porous particles after the clathrates are removed by sublimation. Zwitterionic glycine has been used as an additive to API directly in solutions prior to spray freeze-drying, in order to prevent aggregation of powders, to enhance their dispersibility and improve air-flow properties. The clathrate-forming spray freeze-drying process in the multi-component system was optimized using low-temperature powder X-ray diffraction and thermal analysis.