Continuing the series on USP, <1229.7> addresses gaseous sterilization. Sterilizing gases are typically used when exposure to other methods (heat or radiation) could damage the materials or equipment. The most common gases used for sterilization include ethylene oxide (EO), ozone, mixed oxides of nitrogen, and chlorine dioxide. According to USP, “EO’s ability to penetrate through polymers, cellulosics, and other materials allows it to be used for the terminal sterilization of medical devices in their final packaging.”
This chapter goes into detail about the following gas types (USP definitions):
- Ethylene oxide: “a powerful alkylating agent that destroys microorganisms by chemical reaction, primarily with cell DNA. The destructive mechanism largely follows first-order kinetics and depends on concentration, humidity, and temperature.”
- Ozone: “a potent oxidizing agent produced by passing a stream of oxygen or air through a high-voltage electrical field. Ozone is an effective biocidal agent for treatment of water supplies and has demonstrated lethality at concentrations from 2%-10% in air.”
- Chlorine dioxide: “an effective sterilizing gas. Pure chlorine dioxide is metastable and therefore is generated as needed. Chlorine dioxide in noncarcinogenic, nonflammable, and effective at ambient temperatures.”
- Nitrogen dioxide: “a sterilizing gas effective at ambient temperature. Liquid nitrogen dioxide is converted to a gas on introduction to the target chamber. Nitrogen dioxide is nonexplosive and its residues are noncarcinogenic, noncytotoxic, and nonteratogenic.”
Also included in this chapter is information on the validation of gas sterilization, equipment qualification, empty chamber parameter distribution, component and load mapping, biological indicators, process confirmation and microbiological challenge, and routine process control.
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