January 1, 1997

3 Min Read
EtO Sterilizers Must Revalidate When Changing Their Procedures

An MD&DI January 1997 Column

HELP DESK

Device manufacturers face a number of challenges when trying to bringtheir products to market. In addition to designing and manufacturing devices,they must ensure that the devices are adequately sterilized. The sterilizationprocess requires manufacturers to perform such tasks as validation and bioburdenstudies.Marjorie Lang, a consultant with Lang Consulting, Inc. (Minnetonka, MN),instructs readers to revalidate their sterilization processes when changing thelevels of sterilants. She also explains why bioburden studies are necessary fordevices to be sterilized with gamma irradiation.

Q. Our firm plans to change its sterilization procedure to use a10/90 ethylene oxide (EtO)/hydrochlorofluorocarbon (HCFC) cycle instead of a12/88 EtO/Freon cycle. Do we need to revalidate our process, or can we proceed,using this drop-in gas replacement?

A. Companies that make such a change need to revalidate their sterilizationprocess for microbial lethality, package integrity, EtO residual levels, and,depending on the design of some devices, poststerilization performancecharacteristics. The reason for this is that, even though HCFC carrier gaseswere designed to duplicate the chemical inertness and blending characteristicsof Freon, EtO/HCFC mixtures contain slightly less available EtO and possessslightly different physical properties in regard to vapor pressures and boilingpoints. Such differences necessitate the use of lower evacuation levels andhigher process pressures than were typically needed in 12/88 cycles in order toobtain the desired EtO concentration. In some cases, a slightly longer gasexposure time may also be needed. Additionally, unless the sterilization chamberhas been refitted, chamber fill rates may also be affected because of the slightdifference in the amount of heat required for chamber charging.

Q. Why do we have to evaluate product bioburden for devices we intend tosterilize with gamma irradiation? Can't we simply process the devices at a highdose level and assume that the process will result in at least the minimumsterility assurance level?

A. There are two important reasons for matching the level of gamma irradiationto the product bioburden. First, researchers need to determine the amount ofproduct bioburden and demonstrate that it is consistent, so that a baselinenumber is available to calculate the sterility assurance level conferred by thedelivered dose.

Second, gamma irradiation will always cause some change to materials, eitherimmediately or over time, and these changes are best minimized by using as low adose as possible—even if the materials initially appear capable of withstandinga high dose. Because odd radioresistant organisms do exist, and bioburden levelscan spike or drift out of control, sterilizers need to audit doses quarterly toensure that the minimum sterility assurance level is being achieved.

"Help Desk" solicits questions about the design, manufacture, regulation, and sale of medical products and refers them to appropriate experts in the field. A list of topics previously covered can be found in our Help Desk Archives. Send questions to Help Desk, MD&DI, 11444 W. Olympic Blvd., Ste. 900, Los Angeles, CA 90064, fax 310/445-4299, e-mail [email protected]. You can also use our on-line query form.

Although every effort is made to ensure the accuracy of this column, neither the experts nor the editors can guarantee the accuracy of the solutions offered. They also cannot ensure that the proposed answers will work in every situation.

Readers are also encouraged to send comments on the published questions and answers.

Copyright © 1997 Medical Device & Diagnostic Industry

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