Production Freeze-Drying Systems

Freeze-drying systems used in the pharmaceutical industry must fulfil the following conditions  

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Figure 14.7 Production freeze-drying system designed for instaiiation over two floors.

Vaginal tablets containing lactobacilli have been used in order to restore the normal vaginal flora. Formulation of these delivery systems requires specific proceedings in order to provide viability of lactobacilli and stability of the final product. Freeze drying of bacterial suspensions has been tested to obtain lyophilized powders for tablet production [81]. These powders were shown to be processable and tablet production was easy and reproducible. Also, the use of double-layer tablets (fast-release layer and slow-release layer) seems to be an interesting approach to lactobacilli administration. 

Unlike manifold-based or batch drying, bulk drying allows no control of the conditions to which the product is exposed. Usually, the product is removed from the freeze-drying system prior to closure and then packaged in air-tight containers. Bulk drying is usually restricted to stable products scarcely vulnerable to oxygen and moisture. 

To attain good distribution of the gas, the freeze-drying system is evacuated to a rough vacuum with its own vacuum pump system. After sterilisation, the H2O2 saturated steam is decomposed into water and oxygen with the help of a catalyser. There are no other by-products. For this reason, this process can be considered as completely harmless to the environment. 

The next phase of the freeze-drying process entails the application of a vacuum to the system. When the vacuum is established, the temperature is increased, usually to temperatures slightly in excess of 0 °C. This promotes sublimation of the crystalline water, leaving behind a powdered cake of dried material. Once satisfactory drying has been achieved, the product container is sealed. 

Partial gas- or vapor pressures during freeze drying can also be measured by a mass spectrometer, and water vapor pressures by hygrometers, sensitive only for water vapor. Both systems are necessary for development- and analytical work, but in production plants they need only to be used to check or identify process data. 

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