The Importance Of Critical Temperatures In The Freeze Drying Of Pharmaceutical Products

By Clare Ross, Tony Gaster, and Kevin Ward, Biopharma Technology Limited

Every formulation has a critical temperature, below which it should be cooled for complete solidification and maintained below during primary drying in order to prevent processing defects. To design a freeze drying cycle on a rational basis such information should be identified (Pikal 1990, Frank 1990).

Tc - Collapse temperature, this is the temperature at which the material softens to the point of not being able to support its own structure.

Teu - Eutectic temperature, this is the temperature at which the solute material melts, preventing any structure forming after the solvent has been removed.

Tg' - Glass transition, the temperature of the frozen material changes from a brittle to flexible structure.