Doing Aseptic Filling in Barrier Isolators

Production inside barrier isolators is expected to come on-line for some pharmaceutical companies very soon.

by Jenevieve Blair Polin

Once dreamed of as a way to do aseptic filling in any unclassified space, barrier isolation technology fluctuated in the late 1990s as the validation process for some ambitious systems stretched over more than four years. Now, however, FDA approval is imminent for the applications of the leading pharmaceutical firms that have invested tens of millions of dollars in this technology. Over the next six months, high-speed aseptic filling inside barrier isolators, already a reality in Europe, is expected to get under way in the United States.

The Mini Aseptic Filling System (MAFS) from Bosch-TL Systems features a vertical platform that enhances cleanability.

Lack of FDA guidance and concomitant confusion as to validation requirements have also hindered the progress of barrier isolation technology. Richard Friedman, compliance officer for FDA's Center for Drug Evaluation and Research (CDER), says a revision of the 1987 aseptic guideline, which now for the first time will contain a section on barrier isolators, has been drafted. It is under internal FDA review and will soon be issued for public comment.

DEFINITIONS

Friedman says FDA is considering the following working definition of a barrier isolator: "A decontaminated unit supplied with HEPA- or ULPA-filtered air, which provides uncompromised continuous isolation of its interior from the external environment (e.g., surrounding cleanroom air and personnel)."

This definition acknowledges that barrier isolators can be classified as closed or open systems. Depending on the pressure cascade, the emphasis can be on protecting the product or the operator. Only about 5 to 10% of barrier isolators are sold for pharmaceutical-fill finish operations, says Jack P. Lysfjord, vice president, technology and international sales, at Bosch-TL Systems Corp. (Minneapolis), but these applications have captured a lot of the industry's interest and investment capital.

Open Systems. In an open system, vials are fed continuously at high speeds (up to 750 per minute) from a washer and depyrogenation tunnel system through the tunnel exit directly into the isolator, where they are filled and stoppered. The vials then exit the isolator through a mouse hole. Because the mouse holes are open during operation, continuous overpressure of the barrier isolator is the only thing that ensures separation of the environment inside the isolator from the surrounding room air.

Closed Systems. A closed-system isolator, in contrast, is never opened to the surrounding atmosphere during operation. All components are gathered in batches into portable transfer isolators, which dock to the isolator. The components are then moved into the sealed isolator through double-door systems and rapid transfer ports (RTPs). The speed is slower (around 45 vials per minute), and the runs are shorter for a filling line inside such a closed system than for an open system. All filled vials accumulate at the end of the line inside the isolator, and they must be batched out through transfer isolators.

Closed systems are suited for high-value, low-volume products, such as some biopharmaceuticals and vaccines, as well as for clinical testing. They are also used by manufacturers that must completely protect operators from exposure to the product, for instance, a potent cytotoxic drug. When a closed system is used for containment of the product to protect the operator, the pressure cascade is the opposite of that used to maintain aseptic conditions: negative pressure is maintained inside the isolator, so that no air or particulates escape into the surrounding room.

WORKING MODELS

Lysfjord has been instrumental in facilitating the sharing of information among the leading pharmaceutical companies involved with barrier isolator technology, FDA, and equipment manufacturers. He established the Barrier Isolation Technology Conference in 1992, and he continues to cochair it under the auspices of the ISPE once a year in the United States and once a year in Europe. As a result of this collaboration, aseptic filling lines in barrier isolators have evolved considerably over the past 10 years.

The emphasis has been to "get as much mechanism outside of the enclosure as possible, and keep people out," Lysfjord says.

On integrated isolator and filling lines today, the equipment inside is as sleek and streamlined as possible to enhance cleanability, and the machinery is compact to minimize the volume that must be enclosed. In Bosch-TL Systems' Mini Aseptic Filling System (MAFS), the company has actually turned the equipment 90°, so that it is mounted on a vertical platform instead of a horizontal table, to further facilitate cleaning. Bosch-TL Systems has delivered 7 MAFS units so far, to Eli Lilly, Aventis Pasteur, Merck, Pharmacia, and SmithKline Beecham.

"The advancement of electronics in the past decade, with servos and stepper motors and programmable logic controllers (PLCs), means that the machines can be controlled, monitored, and run from the outside and serviced a lot more easily," adds Ron Nicholas, sales manager, eastern region, M&O Perry Industries Inc. (Corona, CA).

ENGINEERING CHALLENGES

Like the engineers at the dawn of the computer age who had to build their own systems and write their own code, mechanical and design engineers have found that barrier isolators require extensive fine-tuning and sometimes reengineering. "I sometimes tell people that what we got was a giant kit, with a lot of assembly and modification required," says Walt Senour, process coordinator, Center for Advanced Sterile Technology, Pharmacia Corp. (Kalamazoo, MI).

Pharmacia has two high-speed continuous aseptic filling lines from Bosch-TL Systems in barrier isolators built by The Baker Co. (Sanford, ME). On the first line, installed in 1997, the vials are filled, and then they accumulate and are transferred to a lyophilizer. FDA approval of Pharmacia's application for use of this process equipment is expected soon. The second line, installed about nine months later, is a solution suspension line, and Pharmacia plans to file an application for use of this equipment in 2001.

"We made our job many times harder by starting with the line that includes all the freeze-dryers and the transport system," Senour says. "If we had done the solution suspension line first, I think we would have been approved quite a while ago." Lysfjord agrees, adding that the more complex the system, the more time-consuming the validation process is bound to be.

Thomas Freund, regulatory affairs associate at Mallinckrodt Inc. (St. Louis), explains their different approach to filling and lyophilizing. They use a system of linked closed isolators and filling equipment, with a maximum batch size of 10,000 vials filled in an eight-hour shift. As vials from one batch are filled, they are transferred to a lyophilizer using a transfer isolator. Six different types of lyophilized drugs are processed on the isolator line. The lyophilized drug is tagged to a radioactive isotope tracer at a nuclear pharmacy. This isolator system, with BOC Edwards Pharmaceutical Systems (Dongen, The Netherlands) filling equipment and isolators from Carlisle Barrier Systems (New Lisbon, WI) and La Calhene Inc. (Rush City, MN), was approved by FDA in April 1998. Mallinckrodt's second closed-isolator line, approved in March 2000, is used for filling syringes with a product for labeling red blood cells.

This rapid transfer port from PurePulse Technologies would be used in a closed-system isolator.

The biggest challenge for many manufacturers is component handling. One complication is the tendency of ultraclean glassware coming from a depyrogenation tunnel to stick together.

Faced with such infeed problems with their original equipment, Senour and his team at Pharmacia engineered a system of accelerating conveyors with an antibridging belt to keep the glass agitated and prevent the formation of locking angles. They have demonstrated this system on their solution suspension line at speeds exceeding 525 vials per minute.

Mark Diehl, senior engineer at Aventis Pasteur (Swiftwater, PA) agrees that glassware can be uncooperative. Large vials are not usually a problem, he says, but "the 2-ml [size] gives us the most difficulties." Small vials are unstable and can fall and cause jams, particularly on the infeed accumulation. Aventis fills vaccines on the equipment at 225 to 260 vials per minute. The barrier was supplied by Bosch-TL Systems.

Furthermore, more thought has been given to ergonomics in the design of each successive generation of equipment. In an older line, such as Aventis's 1996 line, "not everything is accessible from the front gloves," Diehl says, so making necessary adjustments can be challenging.

Many components of the original aseptic filling lines fail to withstand the harsh environment within the isolator, conditions they would never experience in a traditional cleanroom. For example, says Pharmacia's Senour, "We blow 60°C air through the isolator for drying and some of our conditioning steps. We also use 65°C water as part of our rinsing operation." Many of the plastic guides supplied as components of the original equipment deformed under this heat. "We've replaced most of those guides with Teflon-coated, machined-aluminum guides, which work beautifully," he adds.

The heating and cooling also causes considerable expansion and contraction of the large, welded, stainless-steel structure of the isolator. These forces tend to shift the machine out of alignment, making frequent realignment necessary. "The problem that we see most often is a stoppering issue, when the stopper wheel is no longer located directly over the center line of the vials," Senour explains.

Equipment makers have addressed these issues in successive generations of equipment. "We've had to make the necessary changes so that our components will stand up to repeated vapor-phase hydrogen peroxide (VPHP) cycles," says M&O Perry's Nicholas. "We use the required grade of stainless [steel] so we don't get corrosion, and we've had to substitute plastics that can withstand VPHP and not deteriorate or absorb it," he adds.

OVERPRESSURE AND BREACHES

Because the mouse hole in an open-isolator system represents a potential route of contamination, Friedman says, "It is essential to develop and qualify an overpressure that ensures the full separation of the external environment from the internal isolator environment throughout use." Useful steps, he says, include continuous particulate monitoring in the vicinity of the mouse hole and real challenges, including worst-case dynamic conditions that might occur near the mouse hole or other transfer port.

Both manufacturers and FDA are concerned with the possibility of breaches. Many manufacturers are adding uninterruptible power supplies (UPSs) to keep key components running in the event of a loss of power.

One approach is to put a UPS only on the PLC. Pharmacia has UPSs for some controls, mainly those pertaining to the critical process equipment. "Our power supply is very stable here," says Senour. Power outages don't happen often enough to warrant the expense, complexity, and testing of setting up all the backup generators and systems that would be required to make sure that all the heating, ventilating, and air-conditioning (HVAC) for an isolator system continued to run without a hiccup. A loss of pressure in the isolator is an automatic end of campaign."

In Swiftwater, PA, where Aventis Pasteur is located, thunderstorms, snowstorms, and heavy ice make power outages a fact of life. Like Pharmacia, Aventis has two power infeeds to the plant, so if a line goes down completely, the company can switch over to the other feed. More problematic are power blips or flickers caused by a heavy snow-laden tree limb momentarily touching a wire during a snowstorm. To adress this situation, the company has invested in a UPS system that will maintain the environmental integrity of the barrier isolator and the depyrogenation tunnel, as well as continue supplying the control systems, for up to 20 minutes.

Gloves are another possible route of contamination. "We expect that the integrity of gloves will be given daily attention," Friedman says. In addition to visual inspection of the glove by the operator every time it is put on, some method adequately sensitive to detect a leak must be employed, he adds.

This sensitivity of the test may be the sticking point, says Aventis's Diehl. "If you have a very small hole, on the order of 0.020 in., the leak rate of air from the connection on some commercial [leak testers] could be greater than the actual leak rate of that pinhole." Some small holes tend to seal themselves due to the behavior of the glove material. Diehl has designed, validated, and certified his own proprietary system, which operators use before every run.

CLEANING AND DECONTAMINATION

One of the controversies regarding barrier isolators has been the issue of sterility. Industry has now replaced the term sterilize with decontaminate to describe the process that minimizes viable bioburden.

"We consider these systems a great barrier to keep people away from the product," says Mallinckrodt's Freund, "but is every area in an isolator sterile? No. You can't really prove it. We don't treat [isolators] like autoclaves, and that's helped us with the validation," he adds.

Vapor-phase hydrogen peroxide (VPHP) is the decontaminant used most widely. "These are aerosolized chemical agents blown around by fans, so there's not the uniformity, nor the penetration, that steam has," CDER's Friedman says.

Because VPHP is solely a surface sterilant, surfaces must be exposed as much as possible. Manufacturers have addressed this issue by streamlining the equipment design, as discussed previously, but even little details make a difference. "I've seen a number of failures over the years because gloves were sitting on the floor, and this permitted organisms to survive underneath," says Friedman. This problem can be prevented, he says, simply by following adequate written procedures for isolators.

"Cleaning and decontamination go hand in hand," stresses Aventis's Diehl, "because VPHP can't sterilize a soiled surface." He and his team found that the vial carrier belt on their line was responsible for some random positives during early media fills. Soil that spilled on the belt seeped underneath the cleats and the steel belt backing, where cleaning solutions could not reach it. The engineers machined away a lot of material from the steel rail supporting the belt and modified the steel belt and the plastic cleats that hold the vials, making the unit much more accessible to cleaning solutions.

One drawback of VPHP for many years was the lack of a way to quantify the amount of sterilant in the isolator. Guided Wave Process Analytical Systems, an Ocean Optics Co. (El Dorado Hills, CA) offered near-infrared fiber-optic scanning spectrophotometers (NIR probes) for measurement of hydrogen peroxide vapor concentrations, but there was some concern that water added a significant negative or positive bias to the hydrogen peroxide value obtained. Since their identification of the wavelengths for hydrogen peroxide and water, Guided Wave has developed a new, more precise analyzer, the H^₂O^₂ Vapor Monitor, which can monitor continuously and accurately hydrogen peroxide levels from 0.1 to 10.0 mg/l, and water vapor from 1.0 to 50.0 mg/l.

A stock isolator from Carlisle Barrier Systems is paired with a filler from M&O Perry.

Advanced Sterilization Products, a Johnson & Johnson Co., offers a new option for decontaminating barrier isolators. The Isodox sterilization system generates chlorine dioxide gas. The PLC-controlled, utility-based system is housed in a 6 x 6 x 2-in. cabinet, which is not portable. PVC piping carries the chlorine dioxide gas to the target chamber or chambers.

"Because chlorine dioxide is a true gas, it's stable and can be piped long distances, unlike VPHP, which is a vapor that condenses and degrades," explains John Simmons, the company's worldwide business director for scientific and industrial markets. Units have been installed at pharmaceutical manufacturing facilities and are currently in validation.

A DYNAMIC FUTURE

For the growing number of pharmaceutical products that are heat labile or incompatible with radiation, aseptic filling inside a barrier isolator offers the promise of a high degree of sterility assurance without terminal sterilization. Furthermore, isolators offer protection and minimize operator exposure levels for companies producing potent toxic compounds.

Many high-speed aseptic filling lines in barrier isolators should be approved and coming on-line for commercial production in the coming year. The market for closed systems may be closely tied to the market for these open systems. "For companies doing high-speed production in isolators, it will speed validation to do Phase III clinical and pilot-plant production of small batches in closed isolator systems instead of in the traditional cleanroom, which is a different technology," M&O Perry's Nicholas explains. These systems will nodoubt evolve even more quickly and dramatically as industry's experience with them for actual full-scale production grows.