ISO 11137-2:2013 ✓ Most Recent

From the Forward

ISO 11137-2 was prepared by Technical Committee ISO/TC 198, Sterilization of health care products.

This third edition cancels and replaces the second edition (ISO 11137-2:2012), of which it constitutes a minor revision with the following changes:

- addition of the word "and" in 9.1, second paragraph, third sentence;

- addition of the word "not" in 10.3.4.1, third paragraph;

- correction of the language used to describe requirements for interpretation of results during a verification dose experiment in the second paragraph in 7.2.6.2, 7.3.7.2, 9.2.6.3, 9.3.7.3, 9.4.6.3, and 9.5.7.3.

ISO 11137 consists of the following parts, under the general title Sterilization of health care products - Radiation:

- Part 1: Requirements for development, validation and routine control of a sterilization process for medical devices

- Part 2: Establishing the sterilization dose

- Part 3: Guidance on dosimetric aspects

Introduction

This part of ISO 11137 describes methods that can be used to establish the sterilization dose in accordance with one of the two approaches specified in 8.2 of ISO 11137-1:2006. The methods used in these approaches are:

- dose setting to obtain a product-specific dose; - dose substantiation to verify a preselected dose of 25 kGy or 15 kGy.

The basis of the dose setting methods described in this part of ISO 11137 (Methods 1 and 2) owe much to the ideas first propounded by Tallentire[19][20][21]. Subsequently, standardized protocols were developed[10][11], which formed the basis of the dose setting methods detailed in the AAMI Recommended Practice for Sterilization by Gamma Radiation.

Methods 1 and 2 and the associated sterilization dose audit procedures use data derived from the inactivation of the microbial population in its natural state on product. The methods are based on a probability model for the inactivation of microbial populations. The probability model, as applied to bioburden made up of a mixture of various microbial species, assumes that each such species has its own unique D10 value. In the model, the probability that an item will possess a surviving microorganism after exposure to a given dose of radiation is defined in terms of the initial number of microorganisms on the item prior to irradiation and the D10 values of the microorganisms. The methods involve performance of tests of sterility on product items that have received doses of radiation lower than the sterilization dose. The outcome of these tests is used to predict the dose needed to achieve a predetermined sterility assurance level (SAL).

Methods 1 and 2 can also be used to substantiate 25 kGy if, on performing a dose setting exercise, the derived sterilization dose for an SAL of 10-6 is less than or equal to 25 kGy. The basis of the method devised specifically for substantiation of 25 kGy, Method VDmax, was put forward by Kowalski and Tallentire.

Subsequent evaluations involving computational techniques demonstrated that the underlying principles were soundly based and field trials confirmed that Method VDmax is effective in substantiating 25 kGy for a wide variety of medical devices manufactured and assembled in different ways.

A standardized procedure for the use of VDmax for substantiation of a sterilization dose of 25 kGy has been published in the AAMI Technical Information Report Sterilization of health care products - Radiation sterilization - Substantiation of 25 kGy as a sterilization dose - Method VDmax, a text on which the method described herein is largely based. Method VDmax is founded on dose setting Method 1 and, as such, it possesses the high level of conservativeness characteristic of Method 1. In a similar manner to the dose setting methods, it involves performance of tests of sterility on product items that have received a dose of radiation lower than the sterilization dose. The outcomes of these tests are used to substantiate that 25 kGy achieves an SAL of 10-6.

To link the use of VDmax for the substantiation of a particular preselected sterilization dose, the numerical value of the latter, expressed in kilograys, is included as a superscript to the VDmax symbol. Thus, for substantiation of a sterilization dose of 25 kGy, the method is designated Method VDmax25.

Method VDmax15 is based on the same principles as Method VDmax25. The test procedure is similar to that of Method VDmax25, but Method VDmax15 is limited to product with an average bioburden less than or equal to 1,5. The outcomes of the associated tests of sterility are used to substantiate that 15 kGy achieves a sterility assurance level of 10-6.

This part of ISO 11137 also describes methods that can be used to carry out sterilization dose audits in accordance with ISO 11137-1:2006, Clause 12. Following establishment of the sterilization dose, sterilization dose audits are performed routinely to confirm that the sterilization dose continues to achieve the desired SAL.

Scope

This part of ISO 11137 specifies methods for determining the minimum dose needed to achieve a specified requirement for sterility and methods to substantiate the use of 25 kGy or 15 kGy as the sterilization dose to achieve a sterility assurance level, SAL, of 10-6. This part of ISO 11137 also specifies methods of sterilization dose audit used to demonstrate the continued effectiveness of the sterilization dose.

This part of ISO 11137 defines product families for sterilization dose establishment and sterilization dose audit.

Normative references

The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 11137-1:2006, Sterilization of health care products - Radiation - Part 1: Requirements for the development, validation and routine control of a sterilization process for medical devices

ISO 11737-1, Sterilization of medical devices - Microbiological methods - Part 1: Determination of a population of microorganisms on products

ISO 11737-2, Sterilization of medical devices - Microbiological methods - Part 2: Tests of sterility performed in the definition, validation and maintenance of a sterilization process See more