Medical Design Briefs - January 2023 - 6

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Medical devices sterilized with ethylene oxide (EO) gas need to be tested to ensure they do not
pose a toxicological risk to the end user. Many factors impact EO Residual levels following sterilization,
which makes it difficult to determine when a device is safe for public use. To find out more
about the expertise required to establish safe EO Residual levels for medical devices, Medical
Design Briefs recently spoke with Leonard Harris, Manager, Chemistry and Container Testing for
Eurofins Medical Device Testing (Lancaster, PA).
MDB: How does one determine residual solvents versus the
limits listed in ISO 10993-7?
Leonard Harris: The laboratory should
get a concentration based on the completed
testing. Using the extraction
and testing process, the laboratory
should be able to determine a number
that can be reported in milligrams per
device within a certain period of time.
One can then compare the calculated
value to the limits that are listed in ISO
10993-7, along with the flow chart in
Annex C, to determine whether the residual levels are below
the necessary limit.
MDB: How do you proceed with testing in a medical device
that is too large to extract an entire piece of equipment?
Harris: Per ISO 10993-7, you can select a representative portion
of the medical device and then use that portion to extrapolate
what the EO would be for the entire device. It is also important
to make sure that you are testing the appropriate portion of
a large device when conducting your tests. Typically, only the
portion of the device that will be in contact with the patient
is of concern, unless you have a fluid that flows through the
device. In a case such as an IV Bag, or feeding tube, where the
component may not contact the patient, only the EO residuals
that would be extracted from the fluid pathway are of concern.
In these cases, the device may be filled in such a way that only
the fluid pathway is extracted and tested.
MDB: When calculating residual levels for an infusion-tubing
device, should EO residuals be measured for the fluid path
only? Would measuring the EO levels for the surface contact
area be required for the Tolerable Contact Limit (TCL), also?
If so, should this include the outer surface area of the tubing
and the dressing for the device?
Harris: TCL is only required for materials that make surface
contact with the patient. If the outside of the tube makes contact
with the patient, then knowledge of the EO residual levels
would be necessary to determine irritation.
Each device contained within a kit needs its own considerations.
A dressing would only need residual testing based on whether
or not it would be in contact with the patient. The same could be
said for the tubing. However, even if the tubing does not make
contact with a patient, it will still need fluid pathway testing if a
solution is introduced to a patient through the tube.
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Medical Design Briefs, January 2023
MDB: With EO residual testing, does every single test require
that two medical devices be tested at the same time?
For example, two devices will be tested on Day 0, then two
devices will be tested again on Day 1, etc.?
Harris: Due to the variability in EO affinity and the variability
in the testing methods, multiple samples at each time point are
critical to ensure that the results are accurate. Using multiple
samples ensures that sample results are truly representative of
the product. In most cases, the laboratory will request to test
at least three samples at each time point. Discussing sample
requirements with the testing facility is recommended.
MDB: If an EO residual test is required for a 2X EO cycle,
must two continuous EO cycles be performed? Or does it not
matter as long as the device undergoes the two EO cycles?
Harris: This would depend upon the purpose of the testing. If
you are trying to validate for 2X release, then the EO cycles
should be performed as closely together as possible. Running
the cycles closely together would represent the worst-case
scenario for EO residual testing, as the samples would not have
time to dissipate or break down. If you are performing lot release
testing, then this would not matter as you would only need to
show that the individual lot tested meets acceptable limits.
MDB: Once EO residuals are validated and hold times are
set, does that mean you no longer need to think about EO
residuals?
Harris: No, you would still have to think about EO Residuals in
case of a change that might affect the residual levels. A change
to the sterilization cycle itself, a change to the packaging, or
even a change to the materials within the device would lead
you back to the point where you would need to reassess your
ethylene oxide residuals.
To find out more about Eurofins Medical Device Testing, visit
www.eurofins.com/medical-device.

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Medical Design Briefs - January 2023

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