Optimization of solid structural properties of freeze-dried pharmaceutics by freezing process control with ultrasound devices.

本研究旨在探讨药品冷冻干燥过程中冷冻浓缩相的固体结构特性。甘露醇冷冻干燥试验的结果表明，结晶结构（多晶型物）在干燥原液中的分布不均匀，取决于其冷冻条件。当我们在起始制剂中加入模型蛋白质（酶，采用乳酸脱氢酶）时，冻干原液中的酶活性也是不均匀分布的。这清楚地表明，活性差异是由于冻干保护剂的结构性质差异。因此，我们试图简单地通过工艺操作，即冷冻工艺来稳定冻干的酶活性。发现可以控制冰成核事件的超声装置对于控制溶液在冷冻期间的热历史以及控制结晶物质的固体结构是有用的。然而，用冻干保护剂控制溶液中的固体结构并不那么有效。然而，冻干保护剂的结构变化（如溶胶-凝胶转变）的动力学被认为是稳定蛋白质的关键因素。因此，将表现出胶凝特征的物质用作冻干保护剂。事实上，我们发现，冷却方案和溶胶-凝胶转变动力学强烈相关的蛋白质活性。这些结果表明，冷冻干燥的蛋白质药物的稳定性（或活性）将简单地通过在冷冻期间控制固体物质的结构特征的热方案来控制。

This research work on optimization of pharmaceutical freeze-drying process was to investigate solid structural properties that form in the cryo-concentrated phase during freezing. The results from mannitol freeze-drying test concluded that the crystalline structures (polymorphs) were heterogeneously distributed in the dried bulk dependent to its freezing condition. When we add a model protein (enzyme, lactic acid dehydrogenase was employed) in the starting formulation, the enzymatic activity in the freeze-dried bulk was also heterogeneously distributed. It was clearly suggested that the activity variances were due to the structural property variances of the lyoprotectant. We thus had an attempt to stabilize the freeze-dried enzyme activity simply by the process operation, that is, freezing process. It was found that the ultrasound device that can control the ice nucleation event was useful to control thermal history of the solution during freezing, and to control the solid structure of crystalline substances. However, it was not so much effective to control the solid structure in the solution with lyoprotectant. Nevertheless, kinetics of the structural change (such as sol-gel transition) of the lyoprotectant was supposed to be a crucial factor to stabilize protein. A substance that exhibits gelling feature was thus employed as a lyoprotectant. As a matter of fact, we found that the cooling protocol and the sol-gel transition kinetics were strongly correlated to the protein activities. These results indicate that the stability (or activity) of freeze-dried protein pharmaceutics is to be controlled simply by thermal protocols that controls structural characteristics of solid substances during freezing.