Prefilled syringes: glass or polymer?

Prefilled syringes come in many varieties with the most fundamental difference being the material they are made of – glass or polymer. Manufacturer Schott considers how to make the right choice

Glass dominates the prefilled syringe (PFS) market, but the use of polymer is expected to grow in the next few years. Glass’s excellent barrier properties and regulatory ease make it the first choice for drug manufacturers, but polymer’s stability and inert properties, as well as its wide design options, mean it is an attractive choice as well. So drug manufacturers must ask themselves an important question: Is glass or polymer the better material for PFSs?

Each material has its strengths and weaknesses – there’s no outright winner in this debate. The question itself as to which is better can also be misguided. Before analysing the benefits and drawbacks of each material, pharmaceutical developers must take a holistic view of the drug and a patient’s needs to find what works best for a particular application.

Advantages and drawbacks

Both glass and polymer have advantages and drawbacks. Both materials play valuable roles in the PFS market, yet neither is a ‘one size fits all’ solution. Glass is the preferred material for PFSs, but polymer is a superior material for specific applications.

Glass’s barrier properties prevent oxygen and water vapour from interacting with drug compounds. Since glass is used in 95% of PFSs, it is already compatible with different filling machines and allows seamless integration into pharmaceutical companies’ PFS operations. Regulatory authorities have vast experience with this material, allowing for a streamlined pathway to drug approval. Finally, since glass syringes are produced by multiple packaging suppliers, there is lower risk in supply chain.

Glass isn’t perfect. It is more susceptible to breakage if mishandled during manufacturing, processing on filling lines or by an end-user

However, glass isn’t perfect. It is more susceptible to breakage if mishandled during manufacturing, processing on filling lines or by an end-user. The syringe components, as well as the manufacturing process, open the door for extractables and leachables, including sodium leaching or heavy metal release from the glass barrel, tungsten residues from the hot forming process, or contaminants from the glue, needle and other components.

Meanwhile, the adoption of polymer PFSs is growing. Polymer PFSs offer wider design options while ensuring low rates of breakage. Due to its material properties and manufacturing process, polymer is free of heavy metals and tungsten, and could have low or no siliconisation options. On the other hand, polymer has a lower oxygen and gas barrier threshold than glass, which increases the risk of interaction with oxygen-sensitive drugs. It can also be easily scratched if improperly handled, and haze formation and discoloration can occur during the sterilisation process.

Pinpointing a solution

Drug manufacturers would be remiss to jump to conclusions based on these strengths and weaknesses. Before deciding on a solution, they must assess product demands, process requirements, and practitioner and patient needs when selecting a material. Here are three examples in which the intended use of a drug and the filling process are examined and, via a holistic approach, the right solution is determined.

Schott TopPac polymer syringes for Highly Viscous Drugs (HVD)

The first example is the anticoagulant heparin. This is often a self-administered drug, so patient safety and easy integration with safety devices must be considered. As a result, a glass solution continues to be the best option for heparin packaging. An indication of its stability is that glass has been used to house heparin for more than two decades without any major drug and packaging interactions. Additionally, manufacturers can work with multiple suppliers to fulfill their syringe demand and ensure easy regulatory pathways for drug approval.

For dermal fillers (hyaluronic acid), the end-user assessment is quite different. Dermal fillers are used in cosmetic applications to reduce wrinkles, and are often highly viscous substances. For that reason, these substances require packaging design flexibility that allows a consistent gliding force.

Polymer is often used in dermal filler packaging because it is more break-resistant than glass, and can be manufactured for specific sizes, inner diameters, and finger flange designs while maintaining tight tolerances during production. Polymer syringes also feature an integrated Luer lock that prevents leakage, breakage and needle pop-off.

Drug stability

Finally, stability is critical for biotech drugs. While both polymer and glass offer long-term drug stability for biopharma-ceuticals, the material choice is driven by the type of drug and intended use. Glass offers enhanced functionality for end users and streamlined filling on the manufacturing line. And glass glass is well known and accepted by various regulatory authorities as a packaging solution for biotech drugs; yet polymer offers advantages for packaging, including design flexibility, tighter tolerances, and superior break resistance with a better fit in autoinjectors. For biotech applications, the intended use must be assessed before deciding between glass or polymer.

Weighing up the benefits

Drug manufacturers must consider drug-container interactions, machinability, and regulatory compliance when selecting the right material for their PFS application. A decision that ignores these facts can prove harmful to patients. But most important, drug developers must weigh the intended use and needs of patients. These considerations include the PFS’s functionality, drug safety, and ultimately patient comfort.

SCHOTT TopPac polymer syringes for Highly Viscous Drugs (HVD)

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