Many studies have used the co-spray drying method to prepare dry powder formulations containing L-leucine. The study found that the prescription has the following characteristics:
(1) The yield of spray-dried dry powder is related to the amount of leucine added. The spray-dried formula yields of 1% ethanol aqueous solution of carbaladin bitartrate (RHT), inulin (Inu) and L-leucine (Leu) increased with the increase of L-leucine content.
(2) The morphology of the microparticles composed of leucine depends on the proportion of L-leucine in the preparation, and they are generally corrugated spherical particles with a collapsed surface. L-leucine has relatively hydrophobic and surfactant properties. This is related to the presence of a strong hydrophobic alkyl side chain in the leucine molecule. Leucine molecules show surface activity in aqueous solutions and tend to accumulate at the air-solvent interface. In addition, the low solubility of leucine makes it quickly supersaturate when spray drying starts, thereby nucleating on the surface of the dried droplets to form a hydrophobic shell. During the drying process, as the solvent evaporates, the L-leucine on the surface of the droplet cannot shrink quickly, causing the surface to collapse to form a wrinkled outer surface. RHT-Inu-Leu is a dry powder SEM prepared by co-spray drying. It can be seen that the formulations without L-leucine are smooth spherical particles. The crystal habit of dry powder containing leucine is wrinkled or similar to raisin, and the roughness becomes higher with the increase of the amount of leucine.