Annex 1 and sterilisation process: an interview with Tim Sandle

Published: 3-Nov-2022

AM Instruments talks with Tim Sandle, a microbiologist, author and science journalist, known as one of the leading experts in the field

The revision of Annex 1 is requiring a major effort from the life sciences industry; from setting up new processes, to training staff, to managing noncompliance, the industry needs to adapt particularly to new requirements regarding contamination control strategy and the essential elements needed to develop a robust sterility assurance system.

One of the most discussed processes involves autoclaving and the risks associated with it.

AM Instruments talked about it with Tim Sandle, a microbiologist, author and science journalist, known as one of the leading experts in the field:

Overall impact of new Annex 1 in the pharmaceutical industry

"Our interview opens with an assessment of the overall impact of the new Annex 1 on contamination control strategies in the pharmaceutical industry. Dr Tim Sandle, the new Annex 1 revision is distinguished by a “holistic” view of contamination control. What are the most immediate consequences of this new approach?"

Many facilities have developed approaches to contamination control, but the call within the Annex is for pulling everything together to provide a holistic overview of the facility, the rationale, the gaps, the level of risk for each gap, and the remediation steps. A contamination control strategy is a system that considers all the integral elements of pharmaceutical product manufacturing. This is best achieved using quality risk management principles and supporting risk assessments for contamination control and monitoring (the detectability of contamination event).

As a governing ethos, processes, equipment, facilities and manufacturing activities should be managed in accordance with risk management principles that provide a proactive means of identifying, scientifically evaluating and controlling potential risks to quality.

The strategy at each facility will vary, but common themes will include: microbial contamination, cleaning and disinfection, sterility assurance, facility design, chemical and particle contamination.

Outside of the microbial, other forms of contamination that can arise from mix-ups, damaging primary or secondary packaging, distribution problems, and environmental fluctuations. Overall, a focus will need to be with reducing contamination likelihood and cross-contamination potentials. This needs science and technical procedures and controls.

The format would be as one document or series of connected documents developed to reflect the site-wide strategy for minimising contamination control.

Importantly, the strategy should be a living document and be updated in relation to change controls, process development, recurrent deviations and in relation to other quality records.

Challenges in sterilisation processes

"What are the challenges facing the pharmaceutical industry in sterilisation processes with respect to the requirements of the new Annex1?"

Perhaps the most significant change is in relation to equipment sterilisation when used for aseptic processing. The 2017 draft stated that critical surfaces with direct impact need to be sterilised (such as a filling manifold or stopper bowl); however, with the 2020 revision this now requires direct and indirect contact parts to be sterilised. This could present challenges to facilities with both isolators and RABS devices.

There is a specific update for freeze-dried products in terms of freeze-dryers (or lyophilizers). This is for lyophilizers which are manually loaded or manually unloaded. Here the freeze-dryers should be sterilised before each load.

Other important Annex 1 points include the requirement that the feed water to a pure steam (clean steam) generator should be appropriately purified, to achieve the required chemical and endotoxin levels, as assessed by the Water-for-Injections pharmacopeial monitoring and testing requirements. With the chemical requirement, this is because steam used as a direct sterilising agent must not contain additives at a level which could cause contamination of product or equipment. This part of the process needs to be validated. The steam must also consistently meet the parameters for non-condensable gases, dryness value (dryness fraction) and superheat.

The Annex also specifies that each item sterilised needs be inspected for damage, packaging material integrity and moisture on removal from the autoclave. Any item found not to be fit for purpose, either damaged or where there is evidence of a ‘wet load’, should be removed from the manufacturing area and an investigation performed.

On the subject of wet loads, this is the most worrying factor. When steam enters the autoclave chamber and contacts with the product, it is important that the steam collapses (condenses) on the product. This is in order for the heat to be released to the load. However, the formation of water must be discharged through condensate management or re-vaporised in order to prevent contamination of the product. Removal of the excess water is important to prevent insulation of the load from the steam.

We also need to be mindful of pressure and its relationship to temperature. Given that autoclaves destroy microorganisms by direct steam contact at the required temperature and pressure for a specified time, pressure control is important. Poor pressure control can cause variations in steam velocities.

Critical issues in autoclave sterilisation

"What are the main critical issues in autoclave sterilisation processes?"

Some of the key issues are based on the failure modes. Understanding these modes is important for controlling the critical issues. One that stands out is load design. Many companies will use a matrix approach, whereby worst case load configurations are validated with a view to allowing other load combinations to be used without undergoing validation. Here care must be taken with the design of the matrix so that anything relating to the load that can affect the distribution of the incoming steam or which can affect uniformity of temperature is identified and accounted for. The assessment should also take into account anything that can take heat away from the chamber can affect temperature uniformity.

Often mass is used for the matrix. However, there are other factors that can affect sterilisation. These include the shape of the equipment, where narrow pipework or hoses presents a particular challenge in terms of steam penetration (here centre of the length of hose is the most difficult to sterilise); whereas with worst-case location within a bottle, flask or cylinder the worst case is the centre near the bottom of the container.

The orientation of the equipment is also important, and this affects whether the item is capable of free-draining. Where there is uncertainty about what constitutes worst case some initial work can be undertaken thermometrically (heat penetration evaluation tests); this allows data to be collected about heat distribution, and this ‘hard to heat’ study is generally recommended. Account should be taken, with liquid loads, oft the viscosity of the liquid since this can affect heat penetration.

A further factor is the type of material, such as elastomeric materials and stainless steel. If these types of materials are used in combination, then a balance of both may be needed for the worst case. However, if in practice the materials are sterilised separately, this may prompt two types of worst case loads.

Materials: risks of medical paper and Tyvek advantages

"Let’s talk about materials: despite the strong presence of cellulose, many continue to use medical paper. What are the risks and how, with the new Annex 1 is it necessary to deal with them?"

Packaging materials, used to wrap the items to be sterilised, are probably one of the most important parts of the sterilisation process. Packaging provides a protective barrier for the sterile item and prevents it from becoming re-contaminated. When used in aseptic processing, the packaging should be of low particle generation.

Cellulosic paper is not suitable for higher grade cleanrooms, especially due to the potential for fibres to be released. Annex 1 emphasises that products need to be free of visible particulates. Non-autoclaved cellulosic paper is also probe to microbial contamination, given the range of microbes that are capable of cellulose hydrolysis.

An alternative is Tyvek and Tyvek/PET-PP. Tyvek material is made of continuous strong fibres of pure high-density polyethylene, is low linting and free of inherent contaminants that could represent a risk in critical environments.  Tyvek retains its dimensional stability and integrity and maintains its tensile strength, microbial barrier and the required air permeability to enable effective sterilisation.

In making the correct choice, packaging needs to be well designed and of sufficient porosity so that steam can pass through packaging. In addition, packaging should be water repellent to provide a sterile “field.” Furthermore, the packaging material must not change significantly during sterilisation or release any substances that might interfere with the action of the steam.

Autoclave load validation processes

"New Annex 1 requirements will force pharmaceutical manufacturers to revise their autoclave load validation processes."

Validation needs to be designed carefully to avoid failures (or failures with re-validation). The Annex expects a greater level of detail and investigation. Failure to inactivate biological indicators is normally due to inadequate air removal rather than inadequate conditions of temperature and time.

Sometimes failures of re-validation can be attributed to using biological indicators with much higher D-values than those used for the initial validation (where the biological indicators used for the re-validation have a far higher resistance compared with those used for the initial qualification. This could occur, for example, if the initial qualification was performed using a biological indicator with a D-value of 1.5 minutes and the re-qualification executed using a biological indicator with a D-value of 3.0 minutes).

Issues can also arise due to changes to load patterns. How load patterns are assessed such as mass compared with item complexity and configuration, as with tubing.

One issue will be the requirement to more carefully assess the quality of pure steam. There is also a materials piece, in that before any sterilisation process is adopted, the suitability for the product or equipment need to be assessed to make sure it is suitable for the desired sterilising conditions.

Another factor is with the design of the load, as I’ve previously mentioned. Other considerations for the validation design include handling items of a shape where there is the potential for trapped air (and thus difficulties with air removal). There are also items that may not allow steam to penetrate and are thus hard to heat (such as filters, check valves, and small tubing). Plus, there are items where there is potential for condensate collection.

Critical issues of washable products

"How do you evaluate the use of washable products and what, if any, critical issues do you see in this type of choice?"

The key issue with washable products is with the number of times they can be processed and what the impact of this is upon the life-time of the item. Integrity issues and release of particles are two areas of concern, along with other forms of structural weaknesses and discolouration. This relates not only to the washing process but also to sterilisation – both are aggressive processes that can affect the material. The choice of water and the type of sterilisation process and the parameters surrounding this represent important choices to be made, in order to avoid damage and to extend the reprocessing cycle.

It is important to undertake a careful evaluation, and to set an appropriate maximum reprocessing time.


We would like to conclude this interview with a quote from the new Annex 1.

"8.60 The items to be sterilised, other than products in sealed containers, should be dry, wrapped in a material which allows removal of air and penetration of steam and prevents recontamination after sterilisation. All loaded items should be dry upon removal from the steriliser. Load dryness should be confirmed by visual inspection as a part of the sterilisation process acceptance."

The choice of packaging systems becomes of utmost importance for proper alignment with the requirements of the new Annex 1. Indeed, as is clear from the text, and from the interview with Tim Sandle himself, the success of the sterilisation cycle depends on several factors closely related to the selection of the packaging material: only a low degree of particle release, an anti-microbial barrier of maximum effectiveness, a bill that allows uniform steam penetration, and last but not least tear and puncture resistance can ensure a proper autoclave cycle."

Dr Tim Sandle is a pharmaceutical microbiologist, science writer and journalist. He is a chartered biologist and holds a first class honours degree in Applied Biology; a Masters degree in education; and has a doctorate from Keele University.

Interview by Cristina Masciola, AM Instruments – Marketing & Communication Manager

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