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

本研究旨在优化药物冷冻干燥工艺，研究冷冻浓缩过程中形成的固体结构性质。甘露醇冷冻干燥试验结果表明，结晶结构(晶型)随冷冻条件的不同而不同程度地分布于干燥后的块体中。在起始配方中加入模型蛋白(酶、乳酸脱氢酶)后，冻干样品中的酶活力也呈不均匀分布。很明显，活性的差异是由于冻融保护剂的结构性质的差异造成的。因此，我们试图通过简单的工艺操作，即冷冻过程来稳定冻干酶的活性。研究发现，能够控制冰核事件的超声装置有助于控制溶液在冻结过程中的热历史，以及控制结晶物质的固体结构。然而，用冻融保护剂控制溶液中的固体结构效果不佳。然而，冻融保护剂的结构变化(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，使用一种具有凝胶特性的物质作为冻胶保护剂。事实上，我们发现降温程序和溶胶-凝胶转变动力学与蛋白质的活性密切相关。这些结果表明，冷冻干燥蛋白质药物的稳定性(或活性)只需通过控制冷冻过程中固体物质的结构特征的加热方案来控制。

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.