Ethylene oxide (EtO) is, for many products, an effective sterilization agent. It is especially useful for custom procedure kits containing unit dose drugs in hermetically sealed packages and for products which discolor, distort, or otherwise degrade when processed with radiation. The EtO sterilization process normally requires a product conditioning step in which product is placed in a highly humidified area for a specified period of time. This process humidifies the product, allowing the sterilizing agent, ethylene oxide gas, to penetrate more effectively. After pre-humidification, products are exposed to the EtO by being placed in a chamber for several hours. After exposure, products must be "aerated" by sitting in another chamber in which residual gasses which may have clung to the product are allowed to disperse. This step may take up to several days, depending upon the product and the amount of gas absorbed. After EtO processing, products may not be released for use until a laboratory test on biological indicators has been performed. This test may delay release of product by an additional 3-7 days.

Each load of product which is sterilized with ethylene oxide has a biological indicator or "spore" strip included in the product. Upon removal from the EtO chamber, the product cannot be released until a sterility test is performed upon the BI strip to verify destruction of the indicator organism. Products sterilized with ethylene oxide must be packaged in breathable packaging to allow gasses to escape after EtO exposure. While this type of packaging is readily available, it is quite costly. The process of EtO sterilization requires careful control of several parameters for every lot processed. These parameters include time of exposure, humidity, temperature, pressure, EtO gas concentration, and vacuum. Should an abnormal reading in any of these parameters occur, effectiveness of the process may be questioned. Probably the greatest concern for EtO users and providers is evidence of EtO's potential health hazards to plant employees, the environment, and patients. It is suspected that EtO presents a hazard due to its potentially carcinogenic properties. Furthermore, out-gassing of EtO from processing facilities has come under close governmental scrutiny in recent years. The resulting regulations have increased costs for EtO processing providers, and those costs have been necessarily passed along to EtO customers

Gamma irradiation involves exposure of products in their final shipping containers to a radioactive isotope known as Cobalt-60. Cobalt-60 is processed almost exclusively worldwide by the Canadian government and provided to gamma irradiation plants by Nordion International, who processes and packages the isotope in cobalt "pencils". The pencils are shipped, under extremely tight control and under "hazardous materials" shipping regulations, to gamma plants as needed.

The cobalt pencils are housed in "source racks" within the gamma facility. The racks are placed in the gamma cell, and products in their final shipping configurations travel through the cell on a conveyor system. This process takes several hours to complete. Cobalt-60 decays with time, and appropriate cycle timer setting adjustments must be made at the gamma plant to account for the current cobalt inventory quantity. When the cobalt source is sufficiently decayed, the pencils must be replaced. This "re-sourcing" procedure takes several days to complete, during which time the affected gamma cell is rendered inoperable. Upon completion of re-sourcing, dose mapping must be performed on all products which will be irradiated in the cell.

The effect of gamma irradiation to the product microbial population (bioburden) is the same as the effect of electron beam processing. The fundamental difference between gamma and e-beam sterilization is the manner in which the radiation energy is delivered to the material being irradiated.

The irradiation dose provided by a gamma plant is a function of exposure time of the product to the irradiation source (Cobalt-60), and is thus controlled by a timer setting. Products which can be scheduled to run within the same timer setting are most convenient for a gamma plant to process. The dose range which is most often set in gamma plants is approximately 25 to 35 kilogray (kGy). Products which require lower or higher doses than this range frequently must wait until the timer setting is adjusted to accommodate atypical doses. Gamma facilities cannot easily adjust up or down to produce specific dose ranges, and frequently, products which don't necessarily require a 25 kilogray minimum to destroy their inherent bioburden are processed at the higher rate anyway. Because products are exposed to the gamma source for a time period of 4 to 8 hours, the possibility of product degradation in the form of discoloration and/or embrittlement, is increased over other forms of radiation sterilization such as electron beam.

Several other sterilization methods, such as gas plasma, steam, and others are available and/or under development. At this writing, however, these methods do not accommodate large volumes of product packaged in final shipping configurations which are destined for finished goods inventory at the completion of the sterilization process.

  Back to Top