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

"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."