Big Shot: Developments in Prefilled Syringes

Like all consumers, patients and healthcare providers want products that will make their lives easier, and any product that makes administering or taking an injection easier is bound to be popular. It's no wonder, then, that the vast majority of pharmaceutical companies are noting the advantages of prefilled syringes and scrambling to include them in their portfolios.

Prefilled syringes are not a new technology by any means. They debuted during World War II to accommodate the need for on-the-spot, sterile medications in battlefield hospitals. The next big push into the market came when Becton Dickinson and Company (BD, Franklin Lakes, NJ) began supplying glass prefillable syringes to support Dr. Jonas Salks' poliomyelitis vaccination program in the early 1950s. Prefilled syringes continued to be used mostly for delivering insulin or human growth hormone. In the past five years, however, they have really come into their own, becoming not just a desirable product but almost a required product for parenteral makers to offer.

"If you're going to launch a new product with an already competitive indication, it should be filled in a prefilled syringe for success on the market," says Jörg Zimmermann, head of production at Vetter Pharma-Fertigung GmbH & Co. "Most innovative new products, if they're liquid, are going to be in a syringe, when appropriate."

The numbers attest to this: a study conducted by BD and IMS Health shows that the market for prefilled syringes is expected to grow by 12.8% per year. In 2006, about 1.4 billion prefilled syringes were sold, and by 2010 the quantity is expected to top 2.4 billion.

Changes drive increasing interest

The sudden and intense interest in prefilled syringes can be attributed to several changes in the industry.

Ease of use. The market has seen an increase in the number of biotechnology therapies and drug candidates that can only be administered by injection. These new treatments target a wide range of areas such as multiple sclerosis, fertility, osteoperosis, hepatitis, rheumatoid arthritis, cancer, anemia, and hemophilia.

Some biotech-based drugs require frequent injections to be administered by the patients themselves, and it's these patients, according to Michael N. Eakins, principal consultant with Eakins & Associates (West Windsor, NJ), who stand to benefit the most from the ease of use a prefilled syringe offers.

"A prefilled syringe takes out a series of operations, which makes it quicker and easier," notes Eakins. "It's a great advantage from the patient point of view in ease, safety, and training to have a dose all ready to go in a prefilled syringe."

It's patients who are the true driving force behind the demand for prefilled syringes. Measuring out a dose from a vial into a syringe may be time-consuming and pose a risk for error for those with little training. Moreover, diseases such as rheumatoid arthritis often make it difficult or even impossible for patients to hold a vial and withdraw an accurate dose. Pharmaceutical products that started out as a lyophilized formulations have been changed to liquid formulations to be packaged in prefilled syringes. Berlex's (Wayne, NJ) "Betaseron" multiple sclerosis treatment, and the human growth hormones "Norditropin" (Novo Nordisk, Princeton, NJ), and "Nutropin" (Genentech, San Francisco, CA) all have been reformulated from lyophilized to liquid and are now offered in prefilled syringes.

Ease of manufacture. Syringe component suppliers have stepped up to meet the rising demand in ready-to-use units. Stelmi's (Paris, France) ready-to-use plungers and BD's "Hypak SCF" prefillable syringes eliminate the need for washing, depyrogenation, and sterilization at the filling site. Ready-to-use components are washed, EtO or gamma sterilized, and validated for direct use.

Less overfill. One of the greatest benefits is the significant reduction in the amount of product needed to overfill the container. "By using a prefilled syringe, 10, 15, sometimes even 20% of the API can be saved," Zimmerman notes. "With this all-in-one solution, there is no substance loss through refilling. We've had customers that converted from vial to prefilled syringe that were able to scale down their API process because they didn't need as much," Zimmerman continues.

Overfill for a prefilled syringe is significantly less—in the single digits, according to Cory Lewis, director of new business development with Baxter BioPharma Solutions (Bloomington, IN). "When you're talking about bulk drug API that's in the thousands of dollars per gram, there is a true economic savings that companies can yield," he says. A BD study indicated a potential for up to 23% more product dose yield in a prefill compared with a vial, as less product is lost in the transfer from a vial to a syringe.

Design

Glass and plastic. Although plastic prefilled syringes are gaining in popularity in Europe, glass barrels are still preferred in the United States: 99% of the prefillable syringes sold in the US by BD are its Hypak prefillable glass syringe. Glass is heavily favored, primarily because it has been part of the industry for a long period of time.

"The real problem with the plastic is that it is less well known and less well characterized. Glass has been around as a container for drugs since the Egyptian empire," Michael Eakins points out.

Glass prefilled syringes are made of Type I borosilicate glass, the same type that has been used for vials for a long time. The downside to using glass, however, also is well known: Glass contains alkali ions, which can lead to a surface reaction that forms a small amount of sodium hydroxide. After years of observing this effect in glass vials, most pharma companies know what to expect and have devised ways to get around the problem.

Until recently, plastics were not as clear as glass, making it difficult for companies to visually inspect their products for particulates. But recently, more companies have taken an interest in plastics, mainly owing to recent advances in their design and makeup. Original plastic syringes, which were introduced in the early 1990s, were made from polypropylene. Several companies now offer syringe barrels made of cyclic olefin polymer or cyclic olefin copolymer, which is as clear as glass but less heavy and less likely to break. Cyclic olefin plastics also are more resistant than polypropylene to water transmission, which may help lengthen the shelf life of the drug product.

BD, West Pharmaceuticals, and Baxter BioPharma are all developing plastics for prefillable syringes. In 2000, BD launched a plastic prefillable syringe system known as "BD Sterifill SCF," which is transparent, resistant to breakage, and lightweight. Sterifill is composed of BD's "Crystal Clear Polymer," an amorphous, high-performance polycycloolefin. The company also has released its "BD Uniject" single-use, auto-disable prefill injection device, which contains a small, blister reservoir filled with the drug attached to the needle. Squeezing the reservoir releases the drug.

West's Resin Crystal Zenith (CZ) silicone-free syringe system is made of cyclic polyolefin and has high heat resistance and low temperature characteristics. It is also break-resistant and clear.

Awaiting approval is Baxter's most recent development, "Clearshot," which, like Sterifill and CZ, is break resistant, lightweight, and offers high clarity. The process used to produce Clearshot is somewhat unique: the syringe is formed, processed, and sterilized inline. "We start off with a resin pellet and at the end of the line comes a syringe with the drug product, stoppered," says Cory Lewis.

Plastics have a ways to go before they're widely accepted in the pharmaceutical industry, but as more companies produce purer, more glass-like plastics, plastic syringes begin to gain ground. "There has been much more interest in plastics," notes Eakins. "It's quite clear the interest is increasing."

Vetter produces a dual-chamber syringe in which one chamber is filled with lyophilized product and the other is filled with diluent. When the plunger is pressed, the diluent and lyo products mix and can then be injected. The dual-chamber syringe can also be used with powder and liquid or two liquid products. The latter is, as Vetter's Zimmerman says, a niche market, but it can be used for a multi-dose application that requires a preservative but might not be compatible with the protein for storage.

Stoppers. A necessary component of the prefilled syringes is the rubber stopper or plunger, which carries with it its own challenges. Because stoppers are in prolonged contact with the drug, the primary concern is with leachables from the rubber interacting with the drug.

One example is the case of the antianemic "Eprex." Produced by a subsidiary of Johnson & Johnson (New Brunswick, NJ), Eprex was reformulated to eliminate human serum albumin for the European market and then packaged in a prefilled syringe that replaced the uncoated stopper that had been used before with a coated one. The new formulation of the drug interacted with leachables from the stopper and was later linked to pure red cell aphasia (PRCA) in certain patients, leading to severe anemia.

To combat the problems that may arise from interactions between drugs and rubber stoppers, Stelmi has developed high-purity formulations with a low level of extractables for their rubber components. In the late 1990s, Stelmi launched its "UltraPure 6901" formulation adapted to prolonged contact with water for injection. In 2004, as prefilled syringes continued to gain in popularity, the company began producing elastomer-based formulations 6955 from a new elastomer known as BIMS, which is exempt from oligomers and, thus, less prone to leaching into the drug.

Meanwhile, West Pharmaceutical Services (Lionville, PA) is taking a different tack. Rather than retooling the rubber formulation, the company has begun molding a laminate known as "FluroTec" film onto its stoppers. The film acts as a barrier between the stopper and the drug, reducing the amount of leachables going from the rubber stopper to the drug in the syringe.

Protecting product quality

Concern over extractables and leachables is growing. At a recent AAPS conference, extractables and leachables came third in a list of the Ten Hot Topics of 2007, whereas a mere seven years ago, they didn't even make the list. Whether made of glass or plastic, prefilled syringes deserve special attention when it comes to controlling extractables and leachables.

When it began moving one of its protein drugs to a prefilled syringe, Amgen, Inc. (Thousand Oaks, CA) was surprised to notice that the protein was aggregating. After much investigation (and cooperation between Amgen and BD, the manufacturer and supplier of the syringes), the culprit was found to be tungsten, which is used to hold open the fluid channel at the base of the syringe during the manufacture of the glass. The heat used during the molding process vaporized some of the tungsten, which then settled in the glass at the base of the needle. Prolonged exposure of the drug to the tungsten resulted in visible particles in the solution. BD now has the ability to produce a tungsten-free prefilled syringe.

Some drug makers are concerned that plastics pose a greater risk of extractables and leachables. Plastics and resins are composed of many different components and the formulations can easily change, so there is more uncertainty and potential for extractables. When working with plastics, "you have to take more chemicals into consideration, and therefore there are more unknowns because the plastic vendors will not tell you ... the exact formulation because it is proprietary," says Eakins. The uncertainty means that more testing is often necessary when packaging in plastics, and, according to Eakins, "the last thing you want to do is a lot of research on your packaging, it makes the risks even higher."

One method of cutting down on the amount of testing is to improve communication between pharmaceutical manufacturers and the companies supplying them with prefilled syringe components. Most components manufacturers will provide their clients with lists of possible extractables and leachables, thus allowing the pharmaceutical manufacturers to narrow the field when testing their drugs. Robert Swift, principal engineer of Amgen, hopes that the increased communication between suppliers and the biopharmaceutical industry will "allow [pharma] companies to identify and mitigate formulation-container interactions very early in development."

Silicone, however, is one ingredient that's proving very difficult to eliminate. Silicone is used to coat the inside of syringe barrels. Although silicone poses no threat to some drugs, others have exhibited adverse reactions caused by prolonged exposure to it. West Pharmaceutical Services will soon be introducing its resin CZ system, which eliminates the need for silicone. The plunger is coated with FluroTec, which protects the drug from leachables from the rubber and provides the lubrication needed to allow the plunger to move. Other companies are baking on the silicone, and still others are working to reduce the amount of silicone in the barrels to the least amount possible to still allow the plunger to move.

Besides testing for leachables, pharma companies also must test for break-loose and gliding forces for drugs of various viscosities. For those forces to remain low, there must be some sort of lubricant present. Thus, eliminating or reducing the amount of silicone is challenging.

Figure 1: Glass syringes are currently preferred, and innovations in automation and robotics have increased the efficiency and consistency of handling glass prefilled syringes on the processing line. The photo shows automated heat-tunnel unloading of prefilled syringes (courtesy of Vetter Pharma-Fertigung GmbH & Co. KG).

Processing innovations

Increasing interest in prefilled syringes has lead to innovative solutions in filling and stoppering technologies, barrier designs, automated processing and transfer systems, and robotic handling.

Filling and stoppering. Filling and stoppering syringes present a unique set of challenges than those encountered when processing vials.

"The method you choose to fill and stopper a syringe can influence the stability of the drug product, the movement of the product inside the syringe during shipping, and, in some cases, the sterility assurance of the product," says Shawn Kinney, president at Hyaluron Contract Manufacturing (HCM, Burlington, MA).

Vacuum stoppering technology has been available for several years, but vacuum filling is relatively new. Vacuum stoppering has, until recently, only been performed offline, away from the fill line in a vacuum box. Recently, syringe manufacturers have developed vacuum filling and stoppering capabilities online, primarily for viscous products.

Pulling a vacuum through very thin solutions such as water for injection or buffered solutions causes the liquid to boil and splatter. If splattering occurs during the stoppering process, the liquid product may be entrapped in the ribs of the stopper, posing a potential sterility issue.

Successfully removing air from thin solutions does have several advantages, including increased product stability, lack of stopper movement during shipment and post-sterilization processing, and even potentially enhanced sterility assurance of the solution. Hyaluron has patented a bubble-free filling process that eliminates the air inside the syringe. Bubble-free filling is especially beneficial for oxygen-sensitive pharmaceuticals and proteins that are sensitive to a gas-liquid interphase that appears on small gas bubbles inside the syringe.

"Some proteins tend to rearrange themselves such that the hydrophobic groups point up into the gas phase and the hydrophilic amino acids point down into the liquid phase, which causes more rapid degradation, says Kinney. "The presence of a gas bubble, in conjunction with the silicone coating, will further exacerbate protein aggregation."

Other companies are reportedly working on closed-filling systems similar to those used for vials (1).

Barrier systems. The challenges in handling the shape and composition of syringes also are leading to new barrier system designs, specifically isolators and restricted access barrier systems (RABS).

"Traditional cleanrooms are being phased out in exchange for operations within RABS or isolators," says Eric A. Isberg, product manager, Pharmaceutical Operations, Robert Bosch Packaging Technology (Brooklyn Park, MN).

Whereas vials can easily sit on a track and be directed along their sides with relatively simple belts and conveyors, syringes require direct handling (see Figure 2). Syringes are unstable because of their high center of gravity and therefore require specialized transport systems to reduce the risk of breaking or scratching. The finger flange of the syringe can be the most vulnerable, so the handling system must allow space between each unit.

Figure 2: Automated filling lines provide the necessary direct and individual handling of syringes (photo courtesy of Baxter BioPharma Solutions).

Handling. Syringes can be transported using pucks constructed of thermoresistant plastic or stainless steel. The pucks hold the syringes upright as they move them through heat tunnels. Specially designed trays transport the syringes into autoclaves. Traditional lines are designed to hold syringes by the flange, but some experts believe this system poses a risk to breakage.

"We are seeing more systems that have either pucks or systems that hold the syringe throughout the transport systems using vacuums on the starwheel. This allows the syringes to be elevated as needed without being supported on the bottom or by the finger flange" says Isberg.

Syringes may be supplied in bulk (e.g, for plastic syringes), rondo trays (e.g., for flanged syringes), or in nested tubs. Bulk plastic syringes are first sorted before being arranged in a line and must be presterilized by autoclaving. Current state of the art includes automatic handling units for transferring the syringes into the filling line transport system.

Syringes packed in nested tubs have gained much interest. The tubs are packaged sterilized in bags and contain presterilized units. There are still challenges in their handling with isolators, however. First, the tubs must be removed from the outer bag without compromising sterility. In addition, the outside of the tub must be disinfected before it is transferred into a barrier system, the tubs are continuously transferred into and out of the barrier system, the Tyvek lid of each tub must be removed, and the "nest" and tub must be separated (see Figure 3).

Figure 3: This load-lock system for nested tubs is an integrated three-isolator design with optimized mouseholes, pressure cascades to protect the air in the main chamber, sliding partitions within each chamber, biodecontamination within the main chamber, and shared air handling (photo courtesy of Robert Bosch Packaging Technology).

Isolator manufacturers are working toward new designs that will accommodate this process. Isberg points out that nested tubs have had "major implications" on barrier design, including: large custom mouseholes at the inlet at outlet points, pressure and air separation must be maintained, barriers must be compatible with tub disinfection systems, barrier footprints are wider because of the tub transport system, and removal of the Tyvek sheet lids from the barrier chamber. One new robotic system has been designed to remove these sheets from the tub in an ISO 5 environment, eliminating the risk of contamination and particle generation during delidding.

Automation. Moving away from traditional cleanrooms and toward barrier systems requires a greater reliance on automated systems and robotics. Already there is very little human intervention in the process, but more automation could provide greater consistency.

Automation strategies for prefilled syringes include automated loading of lyophilizers, autoclaves, and dry-heat sterilization tunnels as well as robot transfer systems (2).

"Full automation of all syringe processing steps will soon be a reality," predicts Isberg. "Barrier systems must adapt to accommodate new ways to process syringes, including the use of robotics."

Robotic handing units are commercially available and several have already been installed in pharmaceutical companies. Still, there has been some hesitation in the industry about adopting these units into the processing lines.

"There are robotics for all the steps, it's just a matter of getting them more accepted into the industry," says Isberg. "Moving toward automated processes, such as handling nested tubs, provides consistency, and the technology is becoming cheaper and more standardized. You just have to get past the company's fear of automation so they can understand the advantages of it."

Because the entire process can take place inside a barrier system, engineers are redesigning automated equipment to be smaller and narrower so as to provide operators an easy reach across them if necessary. Barrier systems not only protect the product from contamination and product operators from potent compounds, they also may protect operators from the robotics units inside the system. Isolator and RABs systems may be equipped with "light curtains" that detect when operators place their hands in the gloves and shuts the machinery down. Barrier systems are also equipped with various online sensors for fill volume, headspace analysis, particulate detection, and visual inspection.

"Those are all integrated into the filling system," says Isberg. "A lot of this technology wasn't available 10 to 15 years ago."

Reference

1. B. Verjans, J. Thilly, and C. Vandecasserie, "A New Concept in Aseptic Filling: Closed-Vial Technology," Aseptic Processing, supplement to Pharm. Technol. (May 2005).

2. J. Zimmermann, "Advances in Aseptic Manufacturing," presented at PDA Emerging Manufacturing and Quality Control Technologies, San Diego, CA, Jan. 30, 2007.