EtO Compatibility—and More

Medical Device & Diagnostic Industry Magazine
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An MD&DI June 1999 Column

HELP DESK

James M. Gibson, Jr., a sterilization consultant with J. M. Gibson Associates (Odessa, FL), provides information on humidity as it relates to sterilization and discusses the compatibility of Oxyifume 2000 (AlliedSignal, Morristown, NJ).

Why is humidity an important factor in EtO sterilization, and what would happen if there was no humidity?

Historical studies of the death kinetics of EtO sterilization have demonstrated that a relative humidity of 35 to 90% is necessary for effective sterilization. The upper limit has been debated. Humidity is thought to contribute to the penetration of EtO, particularly through the cell walls of microorganisms. Lack of humidity or insufficient time to allow the adequate penetration of humidity can result in an inability to sterilize the products.

How can humidity inside the chamber be measured during the sterilization process? Who are some manufacturers of gas units that can be fixed inside the chambers?

For processes that do not employ parametric release, humidity measurements are typically judged by a rise in pressure after steam injection. Relative humidity can be calculated from steam tables using the chamber temperature and pressure.

A number of companies manufacture electronic sensors for measuring humidity in EtO chambers. They include Phys-Chem (New York City), General Eastern (Woburn, MA), and Vaisala (Woburn, MA), to name only a few. These sensors are hardwired, and some are not intrinsically safe for operation when EtO is present. Degradation of sensor accuracy requires constant verification of the calibration.

There are also self-contained data-logging units that will record temperature and humidity during the cycles. These units have no wires to the chamber's exterior and are small enough to fit into many primary packages. Two suppliers of this type of unit are Sensitech (Beverly, MA) and Datatrace (Lakewood, CO). Such units can also be used exterior to the product loads in the chamber.

Is Oxyifume 2000 compatible with the various types of materials and devices usually sterilized by 100% EtO or CFCs/EtO 88/12?

There have been a few anecdotal stories of plastic components cracking or crazing following exposure to the new HCFC/EtO gas mixtures, as well as the 88/12 CFC/EtO mixture. In many cases, these problems were traced to manufacturing stresses that were relieved by the CFC in the mixture. In general, the conversion to the new HCFC/EtO mixtures seems to have proceeded without problems. However, exposure of materials to a new chemical in sterilant gas mixtures should be thoroughly evaluated. It is typical to expose samples to maximum sterilization conditions—in other words, the highest gas concentration, highest temperature, and longest exposure time.

Susan Edel Satter of Satter & Associates Inc. (Boulder, CO) has coauthored several articles on EtO sterilization for MD&DI in the past year.

What's the compatibility of polyamide materials (nylon)—particularly Zytel 408HS and RTP 225Z—and EtO sterilization?

Nylons are polyamides because of the characteristic amide groups in the backbone chain. Zytel 408H and RTP 225Z are both referred to as nylon 6/6 because each unit of the polymer chain has two six-atom stretches of carbon atoms. Nylon 6 has only one carbon chain of six atoms.

DuPont Engineering Polymers (800/ 441-0575) was contacted for information on Zytel 408HS NC010, both conditioned and dry, but information was unavailable regarding its compatibility with various EtO processes. RTP Co. (800/433-4797) was contacted for information on RTP 225Z. The RTP representative said that this formulation should be EtO compatible but that testing would have to be done to prove it. While nylon is generally considered to be compatible with EtO processes, specific compatibility must be determined after exposing the finished product to the specific EtO cycle intended for routine use. A careful examination of EtO residuals must also be completed. Nylon absorbs low levels of EtO but is slow to desorb it; therefore, the length of desorption time must also be determined.

Is it true that products sterilized by gamma radiation should not be resterilized with EtO because of potential toxic byproducts?

Different product and packaging materials have been successfully validated for both radiation and EtO gas sterilization. However, exposing some materials to EtO after radiation can result in toxic byproducts. Manufacturers of finished devices must determine each product's biocompatibility based on its intended use after being subjected to a full sterilization process, which may include radiation processing followed by one or more EtO processes. In all cases, the product must be validated for materials compatibility, functional efficacy, and biocompatibility following the complete sterilization cycle intended for routine use.

"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.

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