CL-2022-000676 - [2025] EWHC 2486 (Comm)

Fecha: 01-Oct-2025

ISO 11137: Requirements of a Sterilisation Process

15.

The main international standard which is relevant for current purposes is ISO 11137. That is a standard which has a fairly long history. It comes in two major parts:

Part 1: Deals with the requirements for development, validation, and routine control of a sterilisation process for medical devices. In particular it covers:

Definitions, Quality Management system elements, Sterilising agent issues, Process and equipment, process definition, validation (including review and approval of validation), monitoring and control and maintaining process effectiveness;

ii)

It defines:

SAL as “probability of a single viable microorganism occurring on an item after sterilization”;

Sterilisation as “validated process used to render product free from viable microorganisms”;

Sterilisation dose as “minimum dose needed to achieve the specified requirements for sterility”;

Validation as “documented procedure for obtaining, recording and interpreting the results required to establish that a process will consistently yield product complying with predetermined specifications”.

iii)

It sets out requirements for each of the stages described above

“that, if met, will provide a radiation sterilization process intended to sterilize medical devices, that has appropriate microbicidal activity. Furthermore, compliance with the requirements ensures that this activity is both reliable and reproducible so that predictions can be made, with reasonable confidence, that there is a low level of probability of there being a viable microorganism present on product after sterilization.”

Part 2: Deals with establishing a sterilisation dose of radiation for health care products. This document is 85 pages long. It includes guidance as to:

how to select and test a product to establish a sterilisation dose,

ii)

how then to establish the proper dose.

iii)

methods to establish the right dose (using bioburden information) and to audit the dose.

16.

One aspect which came sharply into focus in the evidence was a section of part 7 of the standard on how to obtain a verification dose. This provided as follows (and was to be preceded by establishing an average bioburden of the product in question):

“Obtain the dose for an SAL of 10^-2 from Table 5 using one of the following as the average bioburden:
a)
if a batch average bioburden is two or more times greater than the overall average bioburden, use the highest batch average bioburden, or
b)
if each of the batch average bioburdens is less than two times the overall average bioburden, use the overall average bioburden.
If the average bioburden is not given in Table 5, use the closest tabulated value greater than the average bioburden.
Designate this dose as the verification dose.”

17.

Table 5, which the reader is spared, is entitled “Radiation dose (kGy) required to achieve a given SAL for an average bioburden greater than or equal to 1,0…”. It has columns with average bioburden from 1 to 1,000,000, and columns for SAL 10-2, 10-3, 10-4, 10-5 and 10-6.

18.

After that the standard envisaged:

Testing 100 samples at this dose, and checking them. It is readily apparent how this acts as a functional proxy for testing actual product post delivery.

Obtaining a sterilisation dose by entering the table at the tabulated value equal to the average bioburden and reading the dose necessary to achieve the desired SAL.

19.

In other words, the process envisages testing samples before irradiation of products is commenced in order to get the dose right and for the dose set to be geared to bioburden.

20.

The standard also has two further parts, not really in focus here, but of some interest. Part 3 provides guidance on dosimetric (measurement of the absorbed radiation dose) aspects during development, validation, and control. Part 4 was only issued in 2020. It offers additional guidance on process control for sterilisation using ionizing radiation; i.e. how to ensure that the process, once established, is robust.

21.

That ISO standard appears to be widely used internationally. But how it is used depends on the relevant local regime. Hence the reference in ISO11137 to “specified requirements for sterility”.

22.

The ISO standard Part 1 notes at 1.2.1 that “This part of ISO 11137 does not detail specified requirements for designating a medical device as sterile. NOTE Attention is drawn to regional and national requirements for designating medical devices as “sterile”. See, for example, EN 556-1 or ANSI/AAMI ST67.”