In the last decade, the use of plastic pre- filled syringes for parenteral administration has been steadily growing. In fact, the compound annual growth rate (CAGR) specific to the plastic segment is estimated to be between 11.5% and 13.8%.

This is understandable when considering and analysing the numerous advantages offered by pre-fillable syringes. Firstly, contamination risks are reduced because fewer steps are required for medication preparation.

This allows for direct drug administration to the patient, avoiding the stages of solution reconstitution and inoculation, and proceeding instead directly with administration. Secondly, pre-fillable syringes allow the operator to inject a dose of medication with high precision, as it is possible to fill the syringe with the exact amount needed for the treatment. This provides advantages in terms of both administration and dosage, avoiding drug waste and facilitating delivery operations.

Glass vs. Plastic Syringes

For decades, glass was the material of choice for pre-fillable syringes due to its high transparency, high chemical resistance, low alkali content, and barrier properties suitable for the long-term storage of vaccines and other pharmaceutical products. On the other hand, glass exhibits high sensitivity to cracking and breakage, as well as the risk of delamination, which constitutes a source of chemical and physical contamination for the drug or substance it contacts.

Furthermore, glass syringes present high levels of tungsten residue near the needle at the Luer Cone connection, which can lead to aggregation phenomena in the case of protein-based drugs. To address these issues, plastic solutions have entered the syringe market – and specifically the pre-filled syringe market – over the last decade.

The most commonly used polymers are:

• Polypropylene (PP)

• Polycarbonates (PC)

• COC (Cyclo-olefin copolymer)

• COP (Cyclo-olefin polymer)

The choice of which plastic to use for a product is directly related to its intended purpose and final use, as well as the intrinsic characteristics of the material. To select the suitable plastic type, one must first consider the final use and the type of solution it will contact.

For a proper evaluation, it is first necessary to identify the “intended use” of the solution or drug the pre-filled syringe will contain. In this initial phase, the syringe is considered primary packaging, and it is then considered a medical device once pre-filled with the solution or drug. To establish the suitability of the plastic, it is necessary to understand how the solution enters into contact with blood or tissues and the duration of exposure.

Based on these characteristics, the plastic must be evaluated for:

• Particulate release

• Biocompatibility

This is to understand the type of interactions that may be triggered, which could lead to drug degradation, protein precipitation (especially for protein-based drugs), decreased shelf-life, and a reduction in the activity of the active ingredient or other components of the solution. For this assessment, various chemical, physical, and biocompatibility tests must be performed to identify the material and particle content in the primary packaging and ensure biological compatibility for enduser safety.