AAMI TIR 76 VDmax SD-S Radiation Validation Overview and Utility for Achieving Product Sterilization Goals
AAMI TIR 76 radiation sterilization validation technical information report was released on March 30, 2021 to expand the utility of the popular VDmax sterilization validation methodology.
This expanded method is known as VDmaxSD-S since it allows for a selection of both the Sterilization Dose (SD) and the Sterility Assurance Level (SAL).
VDmaxSD-S offers the flexibility and lower potential sterilization doses of Method 2 and Method 1, with the convenience and lower sample sizes of VDmax.
VDmaxSD-S still allows for lower dose audit failure risk for certain situations since it is still based on maximal bioburden radiation resistance.
Overall VDmaxSD-S allows more choices for manufacturers to balance product performance, cost and dose audit failure risk compared to Method 1, Method 2, and previous VDmax iterations.
Background: Previous VDmax Iterations, Method 1 and Method 2 Dose Establishment Validations
The Previous VDmax sterilization method iterations (ANSI/AAMI/ISO 11137-2 and ANSI/AAMI/ISO TIR13004) are widely used since they offer the following advantages over Method 1 and Method 2 (ANSI/AAMI/ISO 11137-2, AAMI TIR40).
VDmax consumes less product units for Dose Establishment validation and routine Dose Audits compared to Methods 1 and 2.
VDmax allows for selection of more robust (for inactivating microbes) verification doses under certain conditions than Method 1 and Method 2 to lower risk of dose audit failures. This is because VDmax allows for selection of the verification dose based on assumption of a maximal resistance bioburden resistance rather than using the experimentally determined bioburden resistance (Method 2), or the Standard Resistance (Method 1) for verification and sterilization dose setting.
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These previous VDmax sterilization method iterations have the following disadvantages compared to Method 1 and 2
Only applicable to SAL 10-6
Minimum possible dose even for low bioburden products (below 1.5 CFU) is 15 kGy
Overview of AAMI TIR 76 VDmaxSD-S new features compared to previous VDmax iterations
Allows for selection of SAL 10-3, 10-4, 10-5 or 10-6
Features Sterilization Doses between 3 and 36.4 kGy for the full range of SAL, and 11 to 36.4 kGy for the more common SAL 10-6 in 0.1 kGy increments. This contrasts with previous VDmax iterations which allow dose ranges of 15 to 35 kGy in 2.5 kGy increments.
Sample size for verification dose experiment can be chosen as 10, 30 or 90. The higher sample sizes are available to allow for the option of a more robust sample size to account for bioburden variation among samples. Note that manufacturers have the option to choose a different sample size for dose establishment and dose audits.
Bioburden monitoring frequency is every quarter for products manufactured consistently throughout the year independent of bioburden levels or sterilization dose. In contrast, VDmax 15 and 17.5 kGy require monthly bioburden monitoring under ANSI/AAMI/ISO 11137-2 and ANSI/AAMI/ISO TIR13004 respectively. The rationale for quarterly bioburden monitoring under VDmaxSD-S is that lower bioburden is not correlated with higher variability in bioburden, therefore bioburden monitoring frequency selection should be independent of bioburden level.
2 positives of sterility are acceptable for the verification dose experiment without requiring a confirmatory verification dose experiment as is required by previous VDmax iterations. The rationale for this change relative to previous VDmax iterations is based on Poisson Distribution probabilities that 0,1 or 2 positives are likely outcomes for the verification dose experiment when 1 positive is expected mathematically. This is the same rationale for accepting 0, 1, or 2 positives for Method 1 verification dose experiment.
Rather than using tables to select the verification dose and dose augmentation value outputs based on inputs (bioburden, SAL, SIP and the selected sterilization dose); the TIR 76 utilizes an online calculator since there is an almost infinite number of possibilities that cannot be conveniently captured in tables. See link to online calculator below:
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https://aami.edaptivedocs.org/Tools/AAMIVDmax.aspx
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Dose Establishment Method Comparison: Overview
Dose Establishment Method Comparison Details
TIR 76 Calculation Tool Example: 0.1 CFU Bioburden Corresponding to 11 kGy Minimum Allowable SAL 10-6 Sterilization Dose
The table is a comparison of the Verification Dose and Bioburden Limit outputs based on selecting different Sterilization Doses and Verification Dose N values for a product with a low bioburden of 0.1 CFU. The table shows the versatility of the new VDmax SD-S method. The table data was generated using the online TIR 76 Calculation tool; see link below
