|
|
One application of this low temperature vacuum drying process is to preserve materials that are not stable as “ready-to-use” liquid preparations. Removal of water that may be involved in hydrolysis reactions provides for preservation of quality and purity, providing for long term storage stability in the dried state. Product is returned to a liquid with reconstitution using an appropriate diluent to again form an aqueous solution, suitable for its intended use.
|
The process is comprised of three principle parts: Freezing, Primary Drying and Secondary Drying. Classically described as three separate, unique and interdependent parts of the process, the processing conditions, mechanism, objective and goal are distinctly different for each part. The level of success in achieving the goals of each part has a dominant influence on the success of each subsequent part, as well as the condition and stability of the dried product.
|
|
Critical process parameters are shelf temperature, chamber pressure and time. These process parameters are controlled from the time the product is first placed on the lyophilizer shelves during loading until the product is removed. As an example, conditions reflected in the graph illustrate the process parameters for each respective part.
|
|
|
|
Freezing of the starting dilute solution to subambient temperatures induces solidification, first of the solvent, followed by solidification of the remaining solutes from a more highly concentrated composition. An environment of reduced pressure while the product is maintained at subambient temperature promotes sublimation, converting the ice directly to water vapor, avoiding the return of the composition to the liquid state. This allows drying while retaining the attributes of the frozen preparation. The final amount of water remaining after the ice has sublimed is removed in Secondary Drying. Using conditions at room temperature and above, while maintaining low pressure fosters desorption of the remaining water to achieve low levels of residual moisture and prevent hydrolysis reactions during long term storage.
|
|
