Essentially, freeze drying pharmaceutical consists of three main steps: freezing, primary drying and secondary drying, which includes:
Freezing: The aqueous product undergoes freezing and this is done quickly to prevent large crystals from forming that might rupture the cell walls of the material.
Primary Drying (Sublimation): This is the second phase of the freeze drying process in which pressure is reduced and heat is applied to vaporize the frozen water. This process takes hours to several days to complete depending on the sample. Once primary drying is complete, 93-95% of the water has already been sublimated out.
Secondary Drying (Adsorption): This is the final phase in which temperature is increased even further to remove residual moisture. The remaining water trapped in the solid matrix is desorbed by means of an increase in the temperature.
Freeze-dried pharmaceuticals are then packaged in glass vials with rubber stoppers and aluminum crimping caps.