Formulation-vessel sterilization

The sterilization method for the FV must be decided upon and the process developed. Preservation of sterility following the cycle is equally critical as the act of sterilization. Common sterilization methods that could be employed are autoclave sterilization and SIP. If the FV can fit inside the autoclave, this is the simplest option. If the FV is too large for autoclave sterilization, SIP using steam from the plant's pure-steam system will fulfill the need. SIP is more difficult than autoclave sterilization, and it presents some hazards for operators. SIP will generate substantial humidity in the area where it is being performed. This moisture presents slip–and–fall hazards, and the heat of the external surfaces of the FV can scald.

Regardless of the method chosen, the sterilization cycle needs to be developed for the FV. If autoclave sterilization will be used, the same cycle used to sterilize durable goods may be the most reasonable starting point for FV sterilization. It is suggested to place hydrophobic vent filters on the ports to be used for aseptic connections to facilitate air removal and steam penetration as well as preserving sterility following the autoclave cycle. If vent filters are not used, these connection points will be dead legs, which make air removal and steam penetration more difficult and sterilization less efficient.

The flow of steam through the system needs to be set up to ensure steam penetration and contact with all interior surfaces and product pathways throughout the FV and fittings. Dead legs should be avoided because air can become trapped, thereby reducing sterilization efficiency. When the SIP cycle starts, the steam will condense on the cold interior surfaces of the FV and exit through the outlet ports as water. Once the FV surfaces heat up, the condensate will gradually turn to steam. The inlet and outlet valves need to be adjusted to build the desired internal pressure to achieve sterilization. The valves to the jacket should be opened to prevent the buildup of pressure caused by the temperature increase within the vessel. After the steaming portion is complete, the FV will need to be cooled and dried with a sterile-filtered inert gas. The transition from steam to inert gas should be made gradually while maintaining positive pressure within the FV.

Following the cooling and drying cycle, preservation of sterility is critical. The manner in which sterility is preserved depends on the method of sterilization. If the FV is autoclave sterilized, it will be dried but still quite warm following the cycle. Removing the FV from the autoclave should happen under the protection of unidirectional airflow. Check all clamps for tightness while the FV is still warm. Once the FV cools to room temperature, it can be removed from the unidirectional airflow and stored in lower classification environment until use. The exterior should be sanitized before aseptic formulation begins.

If the FV is SIP sterilized, the following two options exist for preserving sterility:

• Pressurize the FV with sterile-filtered inert gas following the cool-and-dry cycle. All outlet valves will be closed, first the outermost outlet valves and last the inlet valve. All clamps should be tightened. The exterior of the pressurized FV will be sanitized (sanitization method should be qualified). The sanitized FV will be moved into an ISO 5 environment until use. The FV could remain in lower classified environments provided that the internal pressure is maintained until use. If the internal pressure is lost before being placed in an ISO 5 environment, contamination concerns will need to be addressed.
• Pressurize the FV with sterile-filtered inert gas following the cool–and–dry cycle and perform an integrity test of the FV with all fittings. This integrity test will involve closing the valves and measuring the pressure decay as a result of cooling. If the FV has leaks, the pressure loss will be greater than the pressure loss due to cooling alone. Once passing results are obtained, the FV could be stored in a lower classified environment until needed for use. The exterior would still need to be sanitized.