Decision time: Choosing polymer over glass

Polymers are a well-established container material for many drugs. The stability and inert properties, as well as a range of design options, make them an attractive choice. However, the material’s acceptance in parenteral packaging, especially for prefillable syringes (PFSs) is still debated. There is no such thing as ‘one size fits all’. While glass is still the preferred material for PFSs, polymer can also be a valid substitute for specific applications.

While both glass and polymer offer benefits for use in PFSs, for pharmaceutical companies it is often difficult to choose the right material to meet the needs of their drugs and delivery to patients. It very much depends on the drug to be used. German packaging specialist Schott, for example, has put together a list of questions that should be taken into account:

• Does the drug require particularly inert packaging materials?
• How important are design flexibility, tight tolerances, and superior break resistance?
• Do you have to consider integration with safety devices or autoinjectors?
• Does the packaging have to be compatible with different filling machines and ensure easy regulatory pathways for drug approval?
• And, most importantly, is the patient comfort considered and needs met appropriately?

Characteristics

In recent years, polymer PFSs have grown in popularity, as in certain applications they fulfill the requirements better than glass. Polymer offers greater design flexibility while ensuring a low rate of breakage throughout the value chain. Plus, due to its material properties and manufacturing process, polymer is heavy metal and tungsten free, and also features low or no siliconisation.

However, polymer has its own disadvantages. It has a much lower oxygen and gas barrier threshold than glass, increasing the potential for interaction with oxygen-sensitive drugs. Additionally, it exhibits an increased sensitivity to scratches if not handled correctly. Haze formation and discolouration could occur during sterilisation processes.

Compared with polymer, glass shows certain weaknesses. The material is more vulnerable to breakage on the filling line or in the hands of users, if not handled properly. In addition, glass syringe components, as well as the manufacturing process, can 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; and contaminants from adhesives, silicone oil, the needle, and elastomer components. These extractables and leachables could interact with certain drugs and compromise drug stability.

Examples

It’s worth manufacturers understanding the three Ps drug manufacturers bear in mind to assess whether polymer would be a better solution for glass –product needs, process requirements, and practitioner and patient needs. By breaking down the application into these areas, pharmaceutical manufacturers will be able to determine the right material for their PFS.

Some examples provided by packaging expert from Schott will help understand where polymer is a suitable choice:

• Heparin, an injectable anticoagulant, is often used as a self-administration drug. Drug manufacturers need to take into account patient safety and easy integration with safety devices when developing PFS solutions. As a result, a glass solution continues to be the best option for heparin packaging.

• 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 for a consistent gliding force to reduce the force of injection. In addition, polymer syringes have an integrated Luer Lock to prevent leakage and needle pop-off. As a result, polymer tends to be the material of choice for dermal filler packaging. Polymer syringes are more resistant to breakage than glass, and can be engineered for specific sizes, inner diameters, and finger flange designs while maintaining tight tolerances during manufacturing.

• · Biotech drugs – stability is critical for biopharmaceuticals, and for that reason, the drug’s packaging must be selected with care to prevent unwanted interactions. Glass has been a longstanding material in the packaging of injectable pharmaceuticals, especially biotech drugs, and is well known and accepted by various regulatory authorities. However, polymer PFSs could offer advantages for biotech packaging, including design flexibility, tighter tolerances, and break resistance for a better fit with autoinjectors.

To sum it up, while glass is the dominant material used for PFS applications, polymer might also be a viable choice for certain drug applications.