The future of aseptic processing

Dr Douglas Thorogood, Design and Development partner of Isolators for Fabtech Technologies talks about the importance of cleanroom technologies.

In this presentation, I hope to demonstrate a major advancement that has beneficially affected the future of aseptic processing—the advent of isolator technology. Associated with this technology has been the emergence of sterilisation techniques for the isolator and using the gas generators currently available there has also developed gassing techniques for cleanrooms as well.

It is best at the start of this discussion to refer to some definitions that are used today, some of which can be confusing. Historically processes performed in cleanrooms used human operators who were gowned in sterile suits. The products manufactured were defined as aseptic or aseptically produced.

In the field of pharmaceutical science, the words aseptic and sterile are sometimes treated as being synonymous. In microbiological terms the words have different meanings. Aseptic means the absence of pathogenic organisms whereas sterile means the complete absence of life. It is probable that in early cleanroom processing sterility would not be a reasonable expectation due to the presence of human beings, however well trained and gowned the operators may be.

Why use isolator systems as opposed to cleanroom systems for aseptic processing? Well-designed cleanrooms appear to work very well. The answer is complex and is more to do with the culture of the pharmaceutical industry rather than science and engineering. I hope that the following discussion may convince even the most conservative among us that there is no longer any validation or regulatory issue to stand in the way of using isolator technology for aseptic processing. Isolators present us with the best opportunity to remove the presence of operators from the critical processing field and it is possible to contemplate that product assembled or filled under these circumstances are truly sterile. This is due to the fact that the possibility of human borne contamination has been eliminated. It is also possible to deliver reproducible biological decontamination to all of the exposed surfaces inside the isolator and also to make aseptic transfers into and out of the isolator.

Isolator use at present

Pharmaceutical uses for isolators started in 1975. Prior to this time isolators had been used for some limited applications in this field but were mainly focused upon maintaining germ free animals and also for housing immune compromised human beings.

Much of the technical details stemmed from containment technology in the nuclear industry. The aim here was to design isolators for containment. For aseptic processing and sterility testing it was not a great leap of imagination and design to propose systems to keep contamination from getting into the isolator. Half suits as well as glove/sleeve fittings had been derived around this time as well as an adaptation of a rapid transfer port used in the nuclear industry.

The main thrust of the use of the technology was in the field of sterility testing and today there are more than 200 isolators or groups of isolators used for this purpose.

For aseptic processing (around 1975), the first use of the technology for the filling of sterile powders into vials was in Italy. Other developments led to the use of rigid wall isolators, consisting mainly of stainless steel, enclosing a filling machine and also attached to a dry heat-sterilising tunnel. Advances were also made in the field of sterilising the enclosure. Such systems were used to fill cytotoxic products in vials, vaccines into syringes and also other pharmaceutically active but heat labile products into vials, syringes and ampoules. The two most common uses today are for vial filling or syringe filling aseptically using high output filling lines.

Last year a survey was published where it was reported that there were 34 isolator-filling lines in daily production around the world and that the FDA had approved six of them. In Europe EU regulator approvals far exceeds this number. I believe that various isolator manufacturers have delivered more than 95 filling lines to customers around the world. Since the publication last year there have been many additional pre-approval inspections by the FDA and I believe that the number of FDA approved isolator filling systems will rise to around 10 to 15 in the next year.

If we estimate the expansion of the technology, I believe that the number of isolator filling systems purchased will increase by 15 to 20percent per annum over the next several years. My estimate is very conservative but if these figures hold true then it is reasonable to expect isolators to be cGMP by the year 2010.

The above estimates are for the high output filling lines and represent only one application of isolators in aseptic processing. A very large number of isolator systems are in use for investigational drug manufacture, bioprocessing, complex device assembly and sterile implants with sterile adhesive.

Isolator use concerns

The current data on the expansion of isolator uses indicates that the technology has been slow in being adopted for aseptic processing. Many concerns have been expressed but the two major factors have been:

Regulatory approval: It is better to follow than to lead. There still is a belief that it is far safer to follow the path set by earlier users for aseptic processing and to wait until the regulators have approved a number of facilities.

Validation: Lack of international guidelines or performance specifications regarding a number of critical process control/validation issues.

This is largely due to the conservative nature of the pharmaceutical industry in general. New manufacturing technology and systems are slow to be adopted due to the highly regulated nature of the industry.

Europe has a very large number of isolator installations and it is perceived that regulatory bars there to implementation are less imposing. Whilst the FDA offer strong general support for the technology implementation in the USA has been generally slower than in Europe. It may be because the requirements for isolator acceptance were not clear to many potential users. However I believe the period of regulatory uncertainties regarding isolator technology is nearing an end. There has been an increase in the number of pre-approval inspections of isolator systems by the FDA and also an increase in the number of approvals, although much lower than in Europe.

It is expected that the FDA will publish soon their long awaited Guideline for the Production of Sterile Drug Products Produced by Aseptic Processing.

Other documentation to relieve some of the uncertainties regarding isolator technology is as follows:

• The USP has already published a draft revision to the general information chapter. One of the main changes is the inclusion of guidance in the area of isolator design, validation and monitoring
• The PDA has developed a technical monograph on the design and validation of isolators
• The draft ISO standard for the "Aseptic processing of healthcare products" also includes a section on isolator technology
• In the UK there is published a "Guideline to the use of isolator technology"
• In France the A3P group are drafting a French language a practical Guideline for isolator implementers and users of isolator technology
• The Pharmaceutical Inspection Convention (PIC) has offered two drafts of a guideline for the inspection of isolator systems, both for testing and production.

Isolators continue to be installed and validated in Europe. Once Companies have successfully demonstrated that approval of the new technology is achievable other have followed to adopt the new technology. Coupled with these events and also the success that numerous Companies have shown in the validation process (IQ, OQ and PQ) it is apparent to me that the significant obstacles to using isolation technology for aseptic processing is rapidly diminishing.

It is however important to understand the issues most significant for the potential user. In my view the two technical issues for which there are differences of opinion are:

• To preclude ingress of contamination - achieving isolation
• Chemical antimicrobial treatment given to an isolator system to achieve a high level of sterility assurance - decontamination (sterilisation)

Achieving isolation

The most ideal condition to achieve absolute isolation is complete leak tightness. To attain this ideal means in practice specialised, dedicated technology. Generally there are two types of production or testing modes.

• Batch production where the isolator is closed, sterilised and the process completed without opening up the system.
• Continuous production in which materials are continually entering and exiting the system through appropriate openings.

In a recent PDA publication James Agalloco proposed the following definition for such isolators:

Open Isolators: are operated under positive pressure to the external environment and have limited potential for exchange with contaminants from the surrounding environment. Personnel do not directly access the critical zone for set-up and use.

The environment on the inside of the isolator can be sterilised and is of substantially higher microbial quality than the external environment.

Closed Isolators: are operated as a sealed system and do not exchange contaminants with the surrounding environment. Personnel do not access the critical zone during set-up and use.

The environment on the inside of the isolator can be sterilised and is of substantially higher microbial quality than the surrounding environment.

The main difference between the two types of enclosures is that there is at least one opening to the outside environment for the former whilst the latter is sealed. For practical purposes the open isolator is sealed by over-pressure with filtered air. In many cases now isolators are being manufactured with ULPA filters instead of HEPA type filters and in some case with HEPA filters placed before the ultimate ULPA filters.

Differential pressures have been used for many years to maintain air quality zones within cleanrooms and the maintenance of a differential air pressure in an isolator is simpler in that the openings into and out of the isolator are small and they of a fixed size and location. This is not the same picture for large cleanrooms where doors and pass throughs are opened and closed and cause large shifts in pressure relationships that can be difficult to control.

In practice the situation for the open isolator is not complex or difficult to control. It is relatively easy to maintain essentially static air pressure conditions within an isolator. In practical terms it is maintenance of an adequate airflow or velocity through the opening so that a reliable air seal results. Note that it is important that the airflow rate through the opening is not the same as that measured close to the filter face in the isolator. Velocities as low as 0.1 to 0.3 meters per second have been shown to be effective. It is obviously important to demonstrate that the airflow through the opening do not allow eddy currents which may draw contamination into the isolator. It is also important to demonstrate that in using gloves and half suits that air pressure changes are within the acceptance criteria established for the system.

Sterilisation Issues

Unlike cleanrooms the small size and therefore volume of the isolator systems in use today and which can be temporarily sealed are capable of being treated frequently with chemical agents, usually in the form of a vapour or mist, which are used to eliminate microbial contamination, see later in this paper.

Much of the methodology and agents used have been debated regarding the removal of microbial contamination from an isolator system, be it for aseptic processing or for sterility testing. One sees many reports which use such terms as "sterilise the isolator", "sanitise the surfaces exposed in the isolator", and "decontamination". Also some reports add statements implying a sterility assurance level, which can only be attributed to product, which are exposed to a terminal sterilisation process.

I think the industry tends to focus a great deal of attention to terminology and semantics and not enough on the actual desired effect. The later is obviously a reliably sterile and safe product.

Isolators are environments and not product contact surfaces and that the treatment of the environment of an isolator is performed with chemical steriliants periodically. Therefore the microbiological quality of the enclosure is determined by many factors of which sterilisation (or decontamination) is only one. Also remember that the values used to define the performance of a sterilising effect, an S.A.L of 10-6, are really only an assessment of risk.

The guidelines offered at the moment mentioned earlier suggests a "kill" of three to six logs of an appropriate biological monitor. In the choice of the monitor there is much still to be defined, for guideline purposes, as to the characteristics and resistance of the species chosen, currently Geobacillus stearothermophilus or Bacillus subtilis var. globigii (niger).

In my experience decontaminating the isolator environment within this range of "kill" will result in a product that has a very safe level of sterility assurance. This has been borne out many times as shown by data derived from the decontamination of sterility test isolators.

Equally important my experience has taught me that even the most demanding of these requirements can be readily met by way of a well-designed isolator system.

Aseptic transfers

Sterilising dry-heat oven tunnels. These are now used to introduce sterile containers into the isolator at the start of the filling process. There are many variations on the same theme but in essence the junction of the two parts of the system tunnel and isolator can be engineered easily and securely. Airflow generally tends to be adjusted to flow from the isolator into the "clean" end of the tunnel. Doors are now available to close off the entrance to the tunnel when sterilising or decontaminating the isolator.

In many cases of designing an isolator system for high speed filling lines (30,000 to 40,000 vials per hour, as an example) there is the problem of the safe transfer of stoppers, plugs and caps as well as getting sterile containers into the isolator. This also applies to access of the sterile product to be filled.

Components include product contact parts that are conventionally sterilised by team or dry heat. Stoppers, plugs and caps are radiation, gas or steam sterilised. In may cases they are introduced via another isolator attached to an autoclave or dry heat oven and can be passed into the working isolator through the use of a transfer isolator or a dedicated container.

All of the transfers into the environment of the process isolator can be conducted by the use of a double door system, which maintains the sterility of both isolators and isolator/container. They are commonly referred to as Rapid Transfer Systems, usually a door on the isolator and a matching "door" on the transfer isolator or container. A recent introduction has been a dedicated "door" which is used to accept a dedicated container. This container (bag) is disposable. On docking the container but before opening the face of the container is exposed to ultra violet light decontamination There are other variants on the UV theme to gain access to the isolator without compromising the sterility of the enclosure, etc. For pre-packed tubs of sterile syringes there is also now a low power electron beam system that can be attached to the isolator that effectively decontaminates the outside of each tub at a rate of 6 tubs per minute.

In many cases a dedicated steam in place line is connected into the isolator and is sterilised as part of the tank and pipework for the product. Once sterilised the line is opened inside the isolator and connected to the filling line pumps. This avoids making an aseptic connection outside of the isolator environment. Alternatively a modified rapid transfer container is attached to the product tank and steam sterilised in place. The container is then attached to the isolator, the door opened and the filling tube (sterile) attached to the filling line pumps, etc.

The use of the above techniques is expanding and we are gaining more validated data as to the efficacy of the systems in use at present. Again the transfer systems used eliminates the presence of the operator and also ensures sterile connections without fear of extraneous contamination.

Chemical sterilisation or decontamination

Another additional aspect of isolator technology is the ability to be able to decontaminate the isolator environment by using a gaseous or aerosolled chemical agent. These agents are usually powerful oxidising agents such as peracetic acid or hydrogen peroxide although recently there have been tests made using chlorine dioxide and ozone. There have been advances too in the method of delivering these agents and there are now available gas generators, which can be validated to deliver reproducible cycles. In this field there are also devices used to measure the gas concentration, mainly for hydrogen peroxide, with some degree of accuracy and reproducibility, which enables the monitoring of a sterilisation cycle to be more reliable when used in conjunction with biological monitors during the sterilisation cycle validation phase.

Conclusion

At this point in time there are no significant regulatory issues regarding the validation and use of an isolator system to manufacture aseptically filled product. These facts should persuade a pharmaceutical manufacturer to use the technology. Some standards issues need to be resolved but this is equally true with regard to conventional aseptic processing technology. With the latter and using conventional clean room technology could the "clean room" be considered an "endangered" species when compared to the advantages isolator technology can bring to the field of aseptic processing. It is interesting to consider that delayed implementation of isolator techniques may bring about a greater regulatory risk.

Companies that are left behind in the moves to implement isolator techniques for aseptic filling may find that their current processes are no longer cGMP because they will not provide the level of product safety and security that is possible in isolators.