A Sterilization Standard, Different Validation Methods

The ISO 11137 standard is divided into three texts (ISO 11137-1, 11137-2, and 11137-3) which cover all requirements related to the development, validation, and routine control of sterilization processes for medical devices. These texts specifically detail the methods for establishing the sterilizing dose, as well as guidelines related to dosimetric aspects.

The determination of microbial loads and the sterility controls performed before treating products with beta or gamma radiation must comply with the following standards:

• ISO 11737-1 (July 2006), for determining a population of microorganisms (microbial load) on products. This text outlines the requirements to be met for testing samples, validating the dose, and controlling sterilization by irradiation of healthcare products. It also covers irradiation processes using irradiators (using 60Co or 137Cs radionuclides), beta rays (electron beam), or X-rays.
• ISO 11737-2 (January 2010), for sterility controls carried out at the time of defining, validating, and maintaining a sterilization process. It helps to establish the sterilizing dose.

ISO 11137-1: Microbial Load

The ISO 11137-1 standard allows the development of a test to determine the microbial load on a given group of samples.

First, the validation of the microbial load test method must be carried out, which will determine the effectiveness of the chosen sterilization method in eliminating microorganisms. 5 irradiated samples are necessary at this stage. A correction may be made depending on the results.

Once this is done, the microbial load test will determine the number of microorganisms on a product. This step requires testing 30 non-sterile samples distributed across 3 different production batches.

ISO 11137-2: Establishing the Sterilizing Dose

The ISO 11137-2 standard allows the establishment of the sterilizing dose and specifies two distinct methods for determining the minimum dose, as well as for achieving a Sterility Assurance Level (SAL) of 10-6 when a dose of 25kGy or 15kGy is used.

The text also provides methods for auditing the sterilizing dose to monitor its effectiveness over time for a given product.

The validation of the sterilizing dose step determines the minimum radiation dose required to guarantee the desired level of sterility. It takes into account the microbial load present on the product (volume, nature).

The two main methods for determining the minimum dose are called Method 1 and Method 2.

Method 1 involves experimentally testing whether the resistance to radiation of the microbial load on a given product is less than or equal to the average established for a “standard” microbial population. The result will be used as a reference to determine the dose.

The test is performed on 3 batches of 10 samples to achieve a SAL of 10-2. Then, 100 products are irradiated with the verification dose. If 0, 1, or 2 positive samples are obtained, the test is considered conclusive.

Method 2 is generally used when Method 1 cannot be applied. This involves establishing the resistance of the microbial load to radiation by exposing the product to progressively increasing doses. The test is conducted on 3 batches of 20 products.