Re-validation of EO Sterilization – When is re-validation required?

This article reviews some of the factors to consider when you are evaluating the need for EO sterilization re-validation.

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EO Sterilization Cycle Re validation of EO Sterilization   When is re validation required?

ISO 11135-1:2014 is the international standard for sterilization validation for Ethylene Oxide (EO or EtO) sterilizers. The standard describes multiple methods of sterilization validation: 1) overkill approach, 2) single lot release, and 3) parametric release. The overkill approach is the most common method for validation of your EO sterilization process. If you are using a contract sterilizer, the sterilizer will already have completed an Installation Qualification (IQ) and an Operational Qualification (OQ). You will need to complete a Performance Qualification (PQ) for your product. A typical PQ for initial process validation consists of the following:

  1. Process Challenge Device (PCD) validation
  2. Bioburden measurement
  3. EO residual measurement (as per ISO 10993-7:2008/R2012)
  4. Fractional Cycle (at least one)
  5. 3 Half Cycles
  6. 3 Full Cycles (or 1 Full Cycle, if performed in parallel with the three half-cycles)

Most contract sterilizers already have one or more Process Challenge Devices (PCDs) that they have developed, and they may evaluate multiple PCDs in your fractional cycle to determine which PCDs are more challenging to kill than an internal biological indicator (BI). In addition to the above “typical” PQ, you might also choose to validate partial loads and/or re-sterilization of product in the case of rework.

In the ISO 11135 standard, #4 and #5 are referred to as the microbial performance qualification (MPQ), while #6 is referred to as the physical performance qualification (PPQ). For a successful MPQ, at least some of the PCDs must be non-sterile after a fractional cycle to demonstrate the ability to recover the BI challenge organism. After a half-cycle, however, all biological indicators should be sterile.

Ethylene oxide sterilization is typically outsourced to a contract sterilizer due to the environmental and safety requirements of working with EO. Usually, the contract sterilizer will provide a standard validation protocol for full validation that is compliant with ISO 11135-1. However, the ISO 11135-1 standard requires that manufacturers perform annual process reviews to evaluate the need for re-validation of the sterilization process. Assuming there have been no problems, and no changes to the product or process, then re-validation is not required at the end of the first year. However, companies are expected to re-validate the process after two years–even if there have been no changes. So why do some companies perform re-validation after three years or more?

Longer Re-Validation Cycles

If there have been no changes to the sterilization process, the product, or the biological indicators, then the manufacturer can use this as a justification for waiting until two years have elapsed before re-validating the ethylene oxide sterilization process. Also, there should be no evidence of sterilization failures or other problems with the validated process. However, that alone is not necessarily enough to justify extending the duration between validations beyond two years. Companies that can justify intervals of three or more years have multiple products that are using the same sterilization process.

In this case, the manufacturer may alternate annually between three, four, or even five different product families that are using the same sterilization process. In this case, one of the product families is being re-validated each year or every two years, but the interval between validations for any one product family is longer. If the products are made of similar materials and using the same sterilization process, then this approach is valid. If you only have one product, then you need to re-validate the sterilization process once every two years to verify the process remains active.

Minimum Re-Validation Requirements

When you determine that it is time to re-validate your ethylene oxide sterilization process, you need to perform the following tests to meet the minimum requirements of ISO 11135-1:

  1. Re-validation of PCD
  2. Bioburden measurement
  3. EO residual measurement
  4. 1 Half Cycle
  5. 1 Full cycle (to verify the EO residuals are acceptable)

The purpose of #1 is to verify that the resistance of internal BIs used in the half-cycle is more resistant than the product bioburden. The purpose of #2 is to verify that bioburden levels have not changed, and the type of organisms has not changed. In practice, most companies monitor bioburden quarterly, and therefore this step should be routine. Step 3, EO residual measurement, should be performed to verify that there have not been minor changes to the product or process that would increase the concentration of EO, Ethylene Chlorohydrin (ECH), or Ethylene Glycol (EG) beyond the Tolerable Contact Limit (TCL). The purpose of this third test is to prevent localized irritation caused by residual chemicals from the ethylene oxide sterilization process.

Step 4 of the re-validation is intended to verify that a full injection of EO is more than required to kill the bioburden present for the number of injections required for a half-cycle.

The final step is to perform a full cycle. The product from the full cycle is typically used for EO residual testing. Any product from the full cycle that is not used for testing can be sold after sterility testing is complete.

Partial Loads & Rework

If you occasionally sterilize loads that are less than “full loads,” then you need to ensure that you have validated a minimum load or a specific partial load (e.g., half-pallet, instead of a full pallet). In the case of a partial or minimum load, you may identify different locations in your load that is considered “worst-case.” These are the locations that had PCDs that were not sterile in a fractional cycle.

Most companies do not have concerns about the cost of the actual sterilization runs during re-validation, and biological indicators are typically less expensive than boxes of product. The primary cost concern for re-validation is any product that must be scrapped. Therefore, many companies will accumulate dunnage (i.e., empty packaging or scrap product) over time to fill a sterilizer. This dunnage may be used to ensure that every load is a full load, or it may only be used for re-validation.

Another alternative to using dunnage for re-validation is to validate a rework process. Any product that is exposed to a fractional cycle or half-cycle can be resterilized in a full cycle. To justify the commercial use of that product, a company needs to validate that the product will not be damaged by exposure to two full cycles. One of the key acceptance criteria for rework is the EO residual levels in the product. However, the manufacturer also needs to determine if there has been any deterioration of the product by a second exposure to EO that would affect performance.

Other Considerations

Many companies do a poor job of reviewing the potential impact of changes to a product, packaging, and biological indicators. Ideally, initial validation involves different lots of product, packaging, and biological indicators to assess lot-to-lot variability. However, many times, the packaging and biological indicators consist of only one lot during validation. Minor changes to the tolerances may reduce the amount of ethylene oxide that is absorbed by the product or change the resistance o the biological indicator to the sterilization process. Therefore, these minor changes should trigger a re-validation.

Changes in suppliers with the same specification can also be difficult to evaluate. If a component is made of a material that absorbs EO, then it may be recommended to re-validate sterilization for any changes to suppliers of those components. Re-validation in these cases may consist of only a fractional cycle, half cycle, or a full-cycle to evaluate risks associated with the change.

Who Should Be Making Evaluations

The evaluation of the need for re-validation should include the input of three types: 1) microbiological, 2) materials, and 3) performance. To make these assessments, typically, a cross-functional team is needed. Someone with responsibility for design and development can assess the performance impact of changes. A materials engineer is generally needed for assessment of the interaction between components and EO. Finally, a microbiologist is needed to confirm that there is no impact related to biological indicators or bioburden.

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If you need assistance with sterilization validation or bioburden failure analysis, please contact me by email at or call me at +1.802.281.4381.


18 thoughts on “Re-validation of EO Sterilization – When is re-validation required?”

  1. Jayasheel Hegde

    A very good article. It is very important to conduct a re-validation whenever a product packaging is modified or changed. You have made it very clear in this article.

  2. Giovanni Sanchez

    When calculate the TCL for a permanent device, you should use the results of the exhaustive (24 hrs extraction) or you can use an extra test results with 8 hrs extraction?


  3. Hi! I would like to know references to below statement.
    “Any product that is exposed to a fractional cycle or half-cycle can be resterilized in a full cycle. In order to justify the commercial use of that product, a company needs to validate that the product will not be damaged by exposure to two full cycles.”

    In the case of someone need to repeat the sterilization, do we need to validate up to 3x exposure to full cuycles.


    1. Thank you for your question Roslan. There is no “reference” for that statement. It is a scientific rationale: the risk of exposure to the extra fractional or half-cycle is no worse than the exposure to two (2) full cycles. Therefore, if you validate the product is not damaged by exposure to two (2) full cycles, then the product should also be undamaged by 1.5 cycles. The other advantage of validating two (2) full cycles, is that you can re-sterilize product if necessary. Validating a 3x exposure is not needed.

  4. Manuel Graulich

    Good article! Where did you find the requirement of performing EO residual studies in re-qualification (or “re-validation”)?
    Best wishes

    1. Great question Manuel. When you perform your annual review of the process, if there is a shift in products sterilized, this can impact the absorption of EO gas. If there is no change in the products sterilized, then this would not need to be repeated.

  5. Helpful article! I just had a quick question. Is there a reference to this statement, “However, companies are expected to re-validate the process after two years–even if there have been no changes.”?

    1. Yes, but the re-validation is abbreviated, and the standard explains the rationale behind the need for re-validation. Essentially, the biggest risk is a change in bioburden fluora that you are trying to kill due to the selective pressure applied by using cleaning and disinfection methods in the production areas over months and years. There are also potential unseen changes in the contribution by your suppliers and their facilities.

  6. Dear Sir,
    I would like to know about the re validation of the Eto sterilization.
    We did our Knee implant (UHMPWE ) with Eto sterilization at another center so my question is that do we need to revalidate the Eto sterilization or the sterilization center do the Revalidation?
    Could you please clarify this doubt.

    Thank you.

    1. Yes, you need to provide a scientific justification for why revalidation is not required or revalidate. If both locations were owned by the same company (e.g. Sterigenics), then they may be able to help with a scientific justification. However, if the facilities are different owners it is almost impossible to provide a justification for no revalidation. Even small differences in the chamber will change the effectiveness of the sterilization process and affect where BIs need to be located and how product will be loaded into the chamber.

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  10. Hi, could you help clarify if we use one vendor (intermediate vendor) who contracts EtO to another vendor, would the intermediate vendor be responsible for maintaining any annual revalidation review documents? Or would this solely rely on the manufacturer?

    1. That’s a great question. Usually the company that maintains the technical file and device master record would have the process validation (i.e., sterilization re-validation) records. However, it is possible that you might be outsourcing this to a supplier and they are responsible for it. However, you can’t get CE marking without submitting this data and FDA inspectors would ask for these records. Therefore, even if you outsource the responsibility for the work, you will probably still need to provide copies of the records.

  11. Hi,
    I have a question, in-case the re-validation interval (for the EO sterilization process that has only 1 product) was longer than 2 years, which risk aspects we should evaluate for this deviation?

    1. The revalidation interval should be at least every 2 years–not longer. You should evaluate the need for re-validation annually. All aspects that could effect the safety and effectiveness of the sterilization process and your product should be evaluated for potential impact if they have changed. This includes, but it not limited to: PCDs, bioburden, packaging materials, volume of production, load configuration, maintenance, and repairs.

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