A freeze-drying cycle essentially consists of three distinct phases:
a) Freezing of the solution
b) Primary drying or sublimation
c) Secondary drying
Loading of the filled vials in the chamber, maintenance of vacuum throughout the drying phases, supply of refrigeration during freezing and heat during the drying phases, and completion of the drying cycle by stoppering the dried vials and unloading them out of chamber are some other required actions. For a systematic approach to the development of a suitable freeze-dried product, knowledge of the various stages of the process is necessary.
The target freeze drying process must deliver dry product that is safe, stable, and efficacious. That is, the process must ensure acceptable product quality attributes, such as low residual water content, short reconstitution time, and retention of potency, as well as exhibit pharmaceutical elegance. Since freeze drying is a costly and time intensive process, from an operational point of view, the process should be short, reproducible, and robust. An optimized process that operates within the constraints of the equipment, plant utilities, and appropriate safety margins should be the goal.