Lyophilized powder is a pharmaceutical dosage form obtained by freezing a liquid into a solid state under low-temperature conditions, and subsequently removing the water content through sublimation in a vacuum environment, resulting in a dry powder or solid cake. In the pharmaceutical field, lyophilized injections are powder-based preparations formed by freezing a drug solution into a solid state within a sterile environment, followed by the removal of water via vacuum drying.
The core technical principle underlying this process lies in freezing and sublimation. By combining temperature reduction with vacuum application, this method prevents the degradation of heat-sensitive active substances that would otherwise occur during conventional high-temperature evaporation. The lyophilization process comprises three distinct stages: pre-freezing, primary drying (sublimation drying), and secondary drying (desorption drying). Pre-freezing requires solidifying the sample, typically by lowering the temperature to below -40°C. During primary drying, solid ice is directly sublimated into water vapor under vacuum conditions and subsequently removed; the drying temperature during this stage must be maintained below the product's glass transition temperature or eutectic point. Secondary drying serves to remove residual bound water that remains adsorbed to the product through forces such as hydrogen bonding.