Sterility assurance bioburden determinations

The principles behind the sterilization processes are described in Chapter 20. The choice of method is determined largely by the ability of the formulation and container to withstand the physical stresses applied during the sterilization process. All products intended for sterilization should be manufactured under clean conditions and therefore will be of low microbial content (bioburden) prior to sterilization. Under these conditions, the sterilization process will not be overtaxed and will generally be within the safety limits needed to provide the required level of sterility assurance (Chapter 20). The next section emphasizes parenteral products, but the practices described apply to many other types of sterile product. 

The determinants of sterility assurance that must be considered in determining appropriate treatment levels to achieve particular SALs (in this text it will be assumed that the target SAL is lO ) or in validating existing treatment levels are, therefore, bioburden (microorganisms contaminating the item prior to treatment) and the shape and slope of the survival curve. 

Beside bioburden, the other determinant of sterility assurance is the survival curve and its shape and its slope. It is not correct to assume that all survival curves are of the simple linear type when data is plotted on semilogarithmic graph paper. Three general types of survival curve have been reported, the exponential curve, the shouldered" curve, and the "tailed" curve (Fig. 4). 

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