New applications of the VDmax approach to substantiation of preselected sterilization doses

The VDmax approach for substantiation of 25 kGy has been in use for more than 10 years. VDmax methods are included in ISO 11137-2:2006 and AAMI TIR33:2005. ISO Technical Specification, 13004, is under development that will include sterilization doses from 15 to 35 kGy.For substantiation of a sterilization dose for very low bioburden products, less than or equal to 0.3, values of VDmax have now been derived and tabulated for a sterilization dose of 12.5 kGy.Products have been encountered that have both low bioburden and a relatively low maximum dose. In several situations, existing tabulated VDmax values could not be effectively used; in one such situation, the average bioburden was too high to substantiate a 15 kGy sterilization dose and the use of a 17.5 kGy sterilization dose was not practicable due to the likelihood of exceeding the product's maximum acceptable dose. For this product, values of VDmax were derived and tabulated for substantiation of a 16.1 kGy sterilization dose.Values of VDmax have been derived and tabulated for the substantiation of sterilization doses linked to a sterility assurance level (SAL) of 10−3. To offer a potential alternative to aseptic processing, the notion of using an “aseptic processing equivalent dose”, 10−4 SAL, has been investigated along with the use of alternate model populations for calculation of VDmax values.

► Method VDmax is a safe and reliable method for substantiation of a sterilization dose.
► Values of VDmax have been calculated for a 12.5 kGy sterilization dose.
► Product-specific VDmax values can be calculated for special situations, e.g. VDmax16.1.
► Values of VDmax for SAL values other than 10−6 have been calculated and tabulated.
► VDmax values can be calculated based on alternate model microbial populations.