Traditionally, compounding is performed in a Class II biological safety cabinet (BSC) or RABS, both of which provide a semi-enclosed environment directly accessible by the user with HEPA filtered air of ISO 5 quality over the work area to provide some limited protection to the product being handled. Materials needed for compounding activities being performed inside a BSC or RABS are typically transferred in by wiping with a manually applied biocide which is left on the surface of the materials for a validated contact time.

The advantages of BSCs are that they are relatively low cost, easy to install and easy to use. This is because the operator can place their hands directly inside the work area. RABS can provide better protection as there is a physical barrier between the operator and the enclosure. However, as the internal working area can be open to the surrounding environment with both types of PEC, there is a risk of the product becoming contaminated whilst being handled and there is a risk of the operator being exposed to a potentially hazardous product if it is cytotoxic.

More recently, the compounding industry is shifting towards the use of isolators which are a type of PEC that provide a complete physical barrier between the operator and the process, which substantially reduces the risk to both the product and the operator.

What is an isolator?

According to EU GMP Annex 1, which guides the manufacture of sterile medicinal products both produced and consumed in Europe, an isolator is “An enclosure capable of being subject to reproducible interior bio-decontamination, with an internal work zone meeting Grade A conditions that provides uncompromised, continuous isolation of its interior from the external environment”.

Isolators can have a number of features to maintain Grade A conditions and isolation from the external environment such as:

• Airtight/inflatable seals on all doors
• Interlocks to prevent doors being opened once aseptic conditions have been achieved (following bio-decontamination)
• Unidirectional airflow between 0.36-0.45 m/s (to comply with EU GMP Annex 1 guidance values)
• HEPA filters to cleanup incoming air to Grade A (ISO 5) conditions
• Positive pressure
• Leak/pressure testing of enclosure and gloves separately
• Environmental monitoring systems to confirm that the environment remains aseptic during use
• Airflow and pressure alarms

An isolator situated in a cleanroom

A Comparison between approaches

While BSCs/LAFs and RABS offer some limited protection to operators, isolators can be designed to protect the operator completely from exposure to cytotoxic compounds. This design also has a substantial mitigating impact on the risk of the product/ process becoming contaminated by the operator and surrounding environment, which was demonstrated in a study performed by a cell therapy manufacturer. The manufacturer was conducting a manual aseptic process with open manipulations undertaken in a BSC whilst also conducting an automated process with all operations undertaken in automated equipment or an isolator. This gave them the unique opportunity to compare the two approaches, and the study found that the batch failure rate in the BSC was 10% whereas it was only 3%¹ in the isolator.

Being more advanced and complex than BSCs, isolators do inevitably have a higher capital cost. However, this up front cost can be offset by lower facility running costs.

As isolators are completely sealed from their surrounding environment, they can be situated in a lower grade cleanroom than BSCs. This is outlined in USP 797 Table 5; Summary of Minimum Requirements for Placement of PEC for Compounding Non-HD CSPs², which states that a BSC or LAF must be situated in a Grade B (ISO 7) cleanroom whereas an isolator can be situated in a lower Grade C or D (ISO 8) cleanroom. This can result in substantial savings from:

• Reduced energy bills due to lower capacity HVAC system
• Reduced cleaning and disinfection consumable costs
• Reduced labor resource (for cleaning and disinfection)
• Less gowning
• Less maintenance of the cleanroom
• Increased efficiency of operators as lower gowning means they can work for longer periods of time

In fact, one study which investigated the running costs between different cleanroom grades found that Grade C/D cleanrooms resulted in 30% lower running costs than Grade B cleanrooms³. A further study found that Grade C cleanrooms can cost 78% less to build than Grade B cleanrooms⁴.

Despite the above benefits, it is important to note that isolators do have some downsides in comparison to open PEC environments:

They typically have a higher up front / equipment cost. However, this can be offset by the savings from lowering the cleanroom grade and reduced risk of scrapping of product

Operators must perform their duties through gloves connected to sleeves, which can be more difficult than gloved hands operating directly inside the enclosure. This can lead to less efficient work, slowing down a process. Yet, with the isolator being located in a lower grade cleanroom, operators do not have to wear such restrictive gowning meaning they can work for longer periods of time in more comfortable conditions

Hydrogen peroxide vapor

More recently, isolators are now being equipped with an automated bio-decontamination system, typically utilizing hydrogen peroxide which is distributed into the enclosure in either a vaporized or atomized form, in order to kill microorganisms on surfaces. Hydrogen peroxide has become the decontaminant of choice due to its residue free nature, repeatability, and high efficacy; typically achieving a 6-log sporicidal reduction which is validated with Geobacillus stearothermophilus biological indicators. This technology is used to bio-decontaminate the isolator surfaces after it has been cleaned and closed, prior to starting any compounding activity.

It is also used to target the surfaces of materials being transferred into the isolator, to further reduce the risk of any contamination entering the compounded product that will be administered to the patient.

The main drawback to hydrogen peroxide bio-decontamination is the time it takes. Manually wiping and transferring items into a BSC can potentially only take minutes, whereas the empty system bio-decontamination cycle performed on an isolator can take anywhere from 40 minutes to several hours depending on the size of the system, among other factors.

Although the bio-decontamination cycle is typically between 20-60 minutes depending on load size, this is still potentially longer than the traditional spray and wipe approach utilized in BSCs/LAFs. However, there are options available on the market to overcome this hurdle.

Modular isolators

One of the biggest hurdles to overcome when switching from a BSC/LAF or RABS to an isolator is to maintain the same throughput i.e. number of batches, due to the longer bio-decontamination cycle. This is particularly important in a busy hospital where a large number of batches need to be prepared each day. This hurdle can be overcome by adopting a modular approach to isolator systems. A modular isolator system utilizes a multiple chamber principle whereby one chamber is filled with a small amount of materials needed to process several batches and is bio-decontaminated. These materials are then transferred into an adjacent chamber where the compounding process is conducted, the interconnecting door is closed and whilst the batch is being prepared, the materials required for the next batch are bio-decontaminated in the adjacent chamber. An exit hatch can then be used to take finished product out of the system without losing aseptic conditions inside the process chamber.

Ecolab’s Bioquell Qube modular isolator system with a bio-decontamination chamber on the left, processing chamber in the middle, and transfer device on the right

Key features of a compounding isolator

When selecting an isolator for performing compounding activities it is important to consider a number of factors including:

• Size of the system – Is it sufficient for the required throughput of batches per day?
• Operating pressure – Typically an isolator used to conduct aseptic processes should be maintained at a positive pressure relative to the surrounding room to protect the process, but if handling cytotoxic compounds it should be maintained at negative pressure to protect the operators. If the isolator will be used interchangeably for handling both cytotoxic and non-cytotoxic compounds, then choosing an isolator where the pressure can be adjusted after installation is key.
• Bio-decontamination system – Although hydrogen peroxide has become the primary agent for isolator bio-decontamination systems, the method in which it is introduced, i.e. fogging, misting, spraying, nebulizing, atomizing, vaporizing, can have a significant impact on distribution, efficacy, cycle times, and material compatibility. Vapor is the more favorable method as it results in an even layer of micro-condensation being laid down on all exposed surfaces within the enclosure. By comparison, fogging/misting systems do not achieve the same homogenous distribution as the peroxide is maintained in the liquid phase where it will be subject to the forces of gravity. It is also important to consider the regulatory framework behind bio-decontamination. In North America the decontaminating agent must be registered with the EPA in order to make specific claims against specific microorganisms, whereas in Europe there is the Biocidal Products Regulation (BPR).

In compliance with EU law, the chemical being used to bio-decontaminate the enclosure must be tested and a submission made for it to be authorized for use in the specific enclosure size, product type and application method (e.g. vaporization), in order to make claims against specific microorganisms.

• Leak tightness – This is particularly important when working with cytotoxic compounds as operator safety also becomes a key factor. ISO 10648-2 provides a standard for classifying leak tightness of containment enclosures so is a good benchmark to go by, with an hourly leak rate of < 10-2 (class 3) being the target for pharmacy compounding applications.
• Glove leak testing – Gloves typically represent the highest risk of leakage on an isolator system as they are the weak point. However, they are also the most critical point to protect as there is direct contact between the operator and product which therefore puts both at risk. The key parameter for a glove test is the size of hole it can detect. Ecolab has performed testing to confirm that the glove tester for the Bioquell Qube isolator can detect a hole of 50 microns on the standard latex gloves supplied with the system.
• Air management – For a non-cytotoxic application it is perfectly acceptable to vent the exhaust air from the isolator into the surrounding room. In fact, it is beneficial to do so as this reduces the burden on installing an isolator system from a utilities perspective. However, if handling cytotoxics then it is necessary to connect the exhaust of the isolator system to an appropriate duct to ensure that exhaust air, which may contain cytotoxic compounds that are small enough to pass through the HEPA filters, does not come into contact with operators.
• Environmental monitoring – In such a controlled and high air quality environment that an isolator provides, it is important to monitor the environment. Under EU GMP Annex 1 it is mandatory to monitor for viable particles and continuously for non-viable particles to ensure the environment is consistently maintained at Grade A (ISO 5) conditions. There are also requirements in EU GMP Annex 1 concerning the tube length for the particle counter, so it is important that users of isolators understand these requirements to ensure that the isolator system is compliant.

Regulatory trends

By the very nature of being patient specific, compounded products are not licensed or approved by the regulatory bodies around the world in the same way that a medication created for the mass market is. This means that compounded products are not verified for safety, effectiveness or quality. However, there are of course still some standards to apply to compounded products to ensure that they are safe for the patient and many of these standards promote the use of isolators for compounding activities.

In North America the US Pharmacopoeia provides chapters on pharmacy compounding (795 and 797) that outline the differences between a BSC/LAF, RABs and isolator, and confirm that an isolator can be placed in a lower grade cleanroom due to the superior protection offered. In the United Kingdom, the Health and Safety Executive provides specific guidance on handling cytotoxic drugs within isolators in pharmacies, further endorsing their use.

In 2026, PIC/s guidance for the preparation of medicinal products in healthcare establishments will become mandatory under Belgian law and PIC/s guidance endorses the use of isolators for aseptic processing in their guidance document PI 014-35. Finally, Austria BASG GMP inspectors are publicly stating that isolators with hydrogen peroxide vapor bio-decontamination should preferably be used for compounding pharmacies⁶. So, it is fair to say that there is a strong regulatory trend towards the use of isolators for compounding, particularly when compounding cytotoxic compounds.

Summary

As has been made clear in this article, pharmacy compounding is a critical process to provide patients with custom medications which, in the case of intravenously administered products, must be produced aseptically and, in the case of cytotoxic products, operator protection is also extremely important. It is therefore necessary to consider a number of factors when selecting the type of PEC, such as the local regulations, operator safety and product safety. Is now the time to change to an isolator if you haven’t already?

Learn more about Ecolab Bioquell Qube here!

_{(1) LOPES ADRIANA G ET AL. “COST ANALYSIS OF CELL THERAPY MANUFACTURE: AUTOLOGOUS CELL THERAPIES, PART 1.” BIOPROCESS INTERNATIONAL, TUESDAY 27TH MARCH 2018
(2) USP 797 Pharmaceutical Compounding – Sterile Preparations
(3)Répartition aseptique sous Isolateur ou open RABS, Cahier Pratique, 2011
(4)Costing a cleanroom per square foot, Cleanroom Technology, 28 February
(5) PIC/S Isolators used for aseptic processing and sterility testing, PI 014-3, 25 September 2007
(6) Inspection of sterile manufacturing facilities in Austria, Christina Meissner, GMP Inspector. Presented at ISPE Aseptic Conference 12-13 March, 2024}