Steam Sterilization (Heating in an Autoclave)

This process of thermal sterilization using saturated steam under pressure should be used whenever possible for aqueous preparations and for surgical materials. The process is based on the principle of displacing the air in the sterilizing chamber (autoclave) by saturated steam and continuing the exposure to saturated steam for a period of time sufficient to ensure that the entire articles being sterilized are maintained for an effective combination of time and temperature to ensure sterility. In order to displace air more effectively from the chamber and from within the articles, the sterilization cycle may include air and steam evacuation stages.

The choice of a cycle for any article depends on a number of factors, including the heat lability of the material, knowledge of heat penetration into the articles, and other factors. The reference conditions for aqueous preparations are heating at a minimum of 121°C for 15 minutes. Other combinations of time and temperature may be used provided that it has been satisfactorily demonstrated that the process chosen delivers an adequate and reproducible level of lethality when operating routinely within the established tolerances. The procedures and precautions employed should be such as to give a Sterility Assurance Level (SAL) of 10^-6 or better.

Related: SOP for Testing of Biological Indicators

In establishing the sterilization cycle parameters the F0 concept may be used. The F0 at a particular temperature other than 121°C, is the time (in minutes) required to provide the lethality equivalent to that provided at 121°C for a stated time. In general, for aqueous preparations a microbiologically-validated steam sterilization process that delivers, in total (including the heating up and cooling down phases of the sterilizing cycle), an F0 value of not less than 8 to every container in the autoclave load is considered satisfactory. 

Related: Low Temperature Sterilization Process (115°C)
If a product is especially heated sensitive or in certain circumstances where a process that delivers, in total, an F0 less than 8 is necessary, great care must be taken to ensure that a SAL of 10^-6 or better is consistently achieved.

When surgical materials are sterilized the steam used should neither be superheated nor contain more than 5 percent of entrained moisture. Appropriate steps should be taken to ensure adequate removal of air. Most dressings are conveniently sterilized by maintaining at a temperature of 134°C to 138°C for 3 minutes but other suitable combinations of temperature and time may be used.

Also see: Autoclave Validation in Pharmaceuticals

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