ISO 11607: Worst-case parameters
Worst case parameters for medical devices, sealing parameters and configuration
By Noel Gibbons
Anecto Lead Programme Manager
There is a requirement in ISO 11607 that should be highlighted in relation to the worst case parameters for medical devices, sealing parameters and configuration.
A very good source for this is ISO 16775, which is the guidance on implementing ISO 11607 parts 1 and 2, and the basis for this article.
If we look at the text in ISO 16775, Sections H2, 3 and 4 have the following text:
- 2 Worst-case configuration — Medical Devices
- 3 Worst-case configuration — Sterile Barrier System
- 4 Worst-case configuration — Sterile Barrier System Manufacturing Process
H.2 Worst-case configuration — Medical Devices
In ISO 11607 1:2006, 6.1.6, it states: “When similar medical devices use the same packaging system, a rationale for establishing similarities and identifying the worst-case configuration shall be documented.
As a minimum, the worst-case configuration shall be used to determine compliance with this part of ISO 11607.”
Within medical device product families (i.e. medical devices that are similar but not identical), a common sterile barrier system can be used to protect a variety of medical devices.
“Often, the determination of the worst-case configuration is clear. However, in some cases it may be necessary to test more than one medical device.”
The worst-case is established by identifying the medical device(s) that apply the most stress to the packaging system. The worst-case configuration may be the bulkiest or heaviest item in an otherwise common group of medical devices or an item with the greatest number of fitments or other medical device features.
Often, the determination of the worst-case configuration is clear. However, in some cases it may be necessary to test more than one medical device (e.g. the heaviest medical device as well as the medical device with the most fitments) to ensure that the packaging system has been fully challenged. Properly characterizing and evaluating the worst-case configuration will ensure that the other medical devices in the product family will be appropriately protected by the packaging system.
H.3 Worst-case configuration — Sterile Barrier System
Additional direction regarding worst-case testing is provided in ISO 11607 1:2006, 6.3.4 on packaging system performance testing.
“Performance testing shall be conducted on the worst-case sterile barrier system at the specified process limits of forming and sealing and after exposure to all the specified sterilization processes.”
There are two predominant approaches to addressing the key issues of this section. The first and most common approach utilizes sourcing preformed sterile barrier systems manufactured using a fully validated process.
“By choosing an appropriate sample size from multiple lots, one can be assured… that the full ranges of package characteristics have been represented.”
Sterile barrier systems that have been produced as lots run at typical operating conditions within the validated window as they are tested and evaluated.
By choosing an appropriate sample size from multiple lots (typically three), one can be assured, at a given confidence level, that the full ranges of package characteristics (e.g. seal strength) have been represented. Hence, sample size selection and number of lots to be evaluated are important components of the documented rationale. Numerous reference materials exist to assist in sample size determination.
The second approach involves producing sterile barrier systems at the worst-case conditions of manufacture, generally the extremes of the validated window.
In some cases, sterile barrier systems may be produced at the lowest validated temperature, the lowest validated pressure, and the shortest validated dwell to yield sterile barrier systems with the low-end worst-case seal quality.
“…make the final closure seal at or beyond the specified process limits of sealing to ensure that a worst-case sterile barrier system has been produced.”
Typically, the parameters used to establish the OQ are used to produce the sterile barrier systems needed to assess the packaging system performance. This approach can be costly as specific and separate production runs will need to be performed to create the sterile barrier systems at the worst-case conditions of manufacture.
Under both of these approaches, make the final closure seal (whether on a preformed sterile barrier system, tray/lid system, or via the form fill seal process) at or beyond the specified process limits of sealing to ensure that a worst-case sterile barrier system has been produced.
The approach to achieving compliance to ISO 11607 1 will vary between medical device manufacturers, but in each case the approach chosen should be supported by an appropriate rationale, to be included in the documented package validation protocol. The choice will be dependent on corporate risk policy and economic considerations.
H.4 Worst-case configuration — Sterile Barrier System Manufacturing Process
Worst-case configuration is again discussed in ISO 11607 2:2006, 5.1.5, “When similar preformed sterile barrier systems and sterile barrier system manufacturing processes are validated, a rationale for establishing similarities and identifying the worst-case configuration shall be documented.
As a minimum, the worst-case configuration shall be validated to determine compliance with this part of ISO 11607.” In this case, worst-case configuration applies to the sterile barrier system manufacturing processes not to the medical device itself.
“To ensure that the validation is meaningful for the entire sterile barrier system family, the worst-case configuration(s) for the sterile barrier family need to be identified.”
When validating manufacturing processes, the (preformed) sterile barrier systems may be grouped into families, for example chevron pouches using the same top and bottom materials but of different sizes.
To ensure that the validation is meaningful for the entire sterile barrier system family, the worst-case configuration(s) for the (preformed) sterile barrier family need to be identified. When heat sealing, it is important to look at the extremes of seal area.
For example, both small and large seal areas on pouches’ blister packs present unique challenges and should both be assessed. For thermoformed trays and lids, the total square centimetres in the sealing array (i.e. total square centimetres of seal under the sealing platen) could be considered. This approach allows the impact of over sealing and under sealing as well as temperature and pressure distribution to be assessed.
It is important to also consider that the worst-case package configuration for sealing purposes may not be the same as the worst-case for sterilization validation.
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