Validation of an Autoclave Cycle

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Introduction

Steam sterilizers are used in pharmaceutical manufacturing facilities for reusable parts in aseptic processing. According to multiple regulations, all sterilization processes are to be validated1. Because sterility cannot absolutely be proven, the validation process is critical. There are many points to consider when validating a moist heat sterilization cycle. Due to the complexity of the process, validation can become difficult. To determine what is important, multiple regulations and guidelines should be reviewed to ensure all are being followed based on the product being made.

This blog post will review and recommend an approach to develop a successful sterilization process using a steam sterilizer within pharmaceutical manufacturing. The major work for sterilization cycle development will occur before the performance qualification (PQ) testing, with engineering work after the equipment qualification (IQ/OQ). Developing a well-rounded cycle will ensure a proper sterility assurance level is achieved for every cycle run.

Validation is critical because of the inability to prove the sterility of an item without the item becoming non-sterile during the testing process. Confidence of a sterility assurance level of 10^-6, obtained during validation, will give end users a low probability of a non-sterile item. The engineering work performed to determine the critical process parameters of the sterilization cycle prior to qualification will ensure the cycle is developed correctly, which will allow for less potential of failure during the validation cycles.

Validation Approach to Autoclave Validation for a Steam Sterilizer

Sterilization process validation encompasses not only the physical process qualification step (PQ), but also the work performed around PQ to ensure a process is properly validated. The contamination control strategy (CCS) idea throughout EU Annex 1 looks at all steps and the holistic site function following each part and process in a facility. The process of steam sterilization validation can be looked at through three stages around the validation process:

The different stages of the validation process for steam sterilization can create advantages during the official performance qualification with biological indicators and thermocouples. The process design with all parameters set will allow for less variability and possible failure of the validation.

Before cycle development occurs, the IQOQ of the equipment is required. Installation qualification is placing the machine in the proper location. This part of the qualification ensures the installation was completed looking at each of the connections to ensure all connections and pieces are in place based on the manufacturer’s handbook for the specific piece of equipment. All of the utilities are also confirmed to meet the needs of the equipment, and all safety measures are in place. After the equipment is installed, the operational qualification is completed. This is ensuring the functionality of the equipment. Ensuring all utilities are connected and the equipment will run as expected for the pre-set cycles. This is not looking at the sterility of items and only ensuring the alarms and notifications are functioning properly.

In stage 1, it is important to identify all of the possible parameters for the autoclave cycle and also the other processes that need to be validated around the validation of the sterilization process. This can include items like sterilization wrapping and parameters to limit the amount of condensation generated on the parts in the cycle to limit the drying time of the cycle3. An outside process can be something like a sterile hold time of the parts before use after the sterilization cycle.

For the first step, determining the worst-case items for your maximum load is critical. This can be based on size, material, or the path of steam to contact the part. The size of the part can be challenging based on the bulky or heavy nature that can cause pooling in the item or make it difficult to wrap. There are cases when special holders can be designed to place these larger items, like stopper bowls, to promote draining of any condensation that is generated.

Not only do large parts create a challenge during sterilization, but more difficult items, such as tubing and filling needle assemblies are challenging to demonstrate full steam contact. The difficulty comes from not only air removal but also from steam penetration through the smaller gauge of the needle. Biological indicators and thermocouples are required within the hardest to reach areas for air removal and steam penetration.

These difficult to sterilize items also pose a challenge to wrap. This wrapping can be more of a challenge for the removal of air and penetration of steam. Choosing a well-fitted, reproducible wrapping system reduces the number of outside variables on a sterilization cycle. The reduction of variables can help pinpoint a root cause if a failure occurs. The choice of materials for wrapping is also critical for the unwrapping and aseptic presentation of the sterile part. Arguably, the most critical actions post-sterilization are the avoidance of particles and difficulty of unwrapping that can impact the cleanroom environment and can cause more risk to the part and product. Specifically, with the release of EU Annex 1, the impact of particulates and other sources of contamination will be more closely scrutinized.

The material you choose also needs to ensure hold times can be met based on how long the parts and equipment need to be held sterile before use. The hold times will depend on the microbial barrier of the routine wrapping material, the classification of the space where the parts will be held, and the length of time needed between campaigns from sterilization to use. This initial study can be routinely confirmed using the aseptic process simulation.

With all this information determined, placing thermocouples within the hardest to reach location for testing runs can help to determine the cycle length requirements needed to achieve the expected exposure time. The additional work within the beginning of the cycle development will help with reducing potential failures of biological indicators during the performance qualification (PQ).

When doing pre-testing, the load characteristics can have an impact on the length of the sterilization load. It can take extra time to dry certain materials and separating parts into different loads could make the cycles more efficient. The visualization of potential moisture needs to be incorporated into the cycle development. The cycle development will ensure wet loads are not occurring because of the wrapping or load configuration.

For Stage 2, the performance qualification will be completed. The previous testing and development of the cycle should be used to construct a protocol with the loading patterns, cycle time, temperature and pressure, any air removal pulses (if pre-vacuum), sterilization wrapping, and location of the hardest to sterilize location within each part.

All of the validation specifics should be included in the SOP of the facility. Specifically, the cycle number to be completed for the parts to sterilize and the configuration to place them within the autoclave. Biological indicators will be processed post-sterilization, and the thermocouple data will be confirmed to have reached the specified temperature at each location, for the expected duration. This initial validation should be completed in triplicate cycles3. If a bracketed approach is being used, maximum and minimum loads are to be completed and justification for the bracket and strategy should be recorded in the contamination control strategy and validation.

Stage 3 is the re-validation of the autoclave cycle. If there are no major changes which could include cycle parameters, wrapping, or major PMs or mechanical changes3, a yearly re-validation, consisting of one PQ run, will be sufficient to demonstrate the validated state of the sterilization cycle.

 *This requirement in EN285 discussed equilibrium in the autoclave chamber and within dry good loads. The removal of air and penetration of steam to heat more cavernous and dense objects such as stopper canisters or liquid may require additional time for equilibrium and use different testing times.

Conclusion

There are many variables that are associated with sterilizer validation, some of which require their own validation. All these validations need to be completed and documented in the site Contamination Control Strategy. Taking the holistic view of the process, from wrapping to aseptic presentation, will ensure the autoclave validation is successful and a full re-validation is not required every year. Ensuring the engineering work is thorough before the PQ is completed with BIs and thermocouples will save time during the validation. This will ensure the cycle is developed effectively for the parts that are being sterilized and the PQ will be successful. Recording all this information in the CCS demonstrates the review of all process steps that could impact the cleanroom areas. This will require a thorough understanding of the process and all parts and equipment. Including all the development work during the beginning of the process will help to reduce rework or issues down the road during the autoclave validation process.2

Abbreviations

BI(s): Biological indicator

CCS: Contamination Control Strategy

IQ: Installation Qualification

OQ : Operation Qualification

PQ: Performance Qualification

PM : Preventative Maintenance

SOP : Standard Operating Procedure