Flexible Loading Pattern Approach in Overkill Steam Sterilization Based on the Physical Properties of Steam and Thermodynamics of Sterilization

Abstract

Because overkill steam sterilization processes in autoclaves are considered critical, they are highly scrutinized, and the use of autoclaves in fixed loading patterns is a common approach to the interpretation of regulatory requirements. Many such regulations are attributed to tradition and a buildup of restrictions that aim to improve the levels of assurance of the process and minimize risk. However, these measures complicate the operation and qualification of autoclaves, becoming cumbersome, time-consuming, and costly. In actuality, overkill sterilization is one of several processes in the pharmaceutical industry that provides the highest levels of sterility assurance. This method provides a minimum reduction of highly durable spore populations of 12 logs, achieving a probability of a nonsterile unit (PNSU) of 10⁻⁶. Because these spores are far sturdier than the common microorganisms that can be found in pharmaceutical facilities, overkill sterilization effects significantly lower PNSU values for the latter. The physical properties of steam and the thermodynamics of steam sterilization constitute a predictable and repeatable process that can be monitored and verified. The high assurance level of overkill sterilization, combined with the properties of steam, actualizes a high safety margin that encompasses nearly every load type and load configuration when the cycle is performed under certain basic rules. The aim of this article is to present data that advocate and favor an approach that allows greater freedom and variability in arranging items in an autoclave when running overkill cycles, without the need to qualify each configuration.