Cytotoxicity Testing For Plastics Used In Injectables
How are plastic materials used in injectable products?
Many product-packaging systems use elastomeric materials. Elastomeric materials are plastics that can resume their original shape after experiencing tension or compression. Plastics are used in injectable products such as vials, bottles, prefilled syringes, flexible bags, and blow-fill-seal containers. Stoppers, cap liners, plungers, needle shields, tip caps, seal liners, and injection ports are all examples of injectable product components that utilize plastics. Any plastic with direct or transient contact with a pharmaceutical product or medical product formulation must pass certain regulatory requirements before being used as a device or packaging material. Polymer coatings also fall under the assessment criteria for elastomeric materials. You can find information on these polymers’ composition, manufacturing, and use in USP 1381.
What are the regulatory tests plastic packaging materials used in injectables require?
As mentioned earlier, elastomerics (also known as plastics) in direct or indirect contact with a medical or pharmaceutical product must be assessed for their safety before use. Plastic materials can vary widely in their purity, meaning that intentionally or unintentionally added elements exist in manufactured plastics. Thus, baseline physiochemical and biological reactivity requirements for plastics used in injectable packaging-delivery systems must be met, in addition to functional requirements. Depending upon the elastomeric material, USP 1663 extractables testing may be needed. Overall, plastic safety tests fall under two primary categories: package integrity testing (e.g., functionality, seal quality, and leak testing) and cytotoxicity testing (e.g., biological reactivity and physiochemical testing).
What are cytotoxicity and cytotoxicity testing?
Cytotoxicity refers to molecules and compounds that are poisonous to living cells. Cytotoxins are often chemical but can also be from natural or biological sources. Cytotoxicity testing evaluates the biological reactivity of mammalian cells and tissues to contact with elastomeric plastics, excipients, and other materials that will come in direct or indirect patient contact during medical product use. Thus, sometimes cytotoxicity testing is referred to as biological reactivity testing. Cytotoxicity is significant as it evaluates the biological effects of a sample’s leachable chemicals. The types of cytotoxicity testing to perform for your medical device or product depend upon the final product, the final product’s intended use, and the materials the final product is made of and packaged within.
How are cytotoxicity tests for elastomeric plastics performed?
The following cytotoxicity tests cover both types I and II elastomeric plastics. Nearly all plastics used for injectable, parenteral, and medical products will only require in-vitro cytotoxicity testing covered by USP 87. However, if elastomeric components do not meet the requirements of USP 87 direct contact, agar diffusion, and elution testing, in-vivo cytotoxicity testing outlined in USP 88 will be needed. Either intracutaneous or systemic injection tests can be used for in-vivo testing of elastomers.
What is in-vitro direct contact testing?
Direct contact cytotoxicity tests can evaluate nearly all materials. Additionally, sample extraction and testing of a sample’s leachable chemicals can occur simultaneously with direct contact testing. Direct contact methods cannot assess very low density or extremely high-density materials that could cause mechanical damage to cultured live cells.
What is in-vitro agar diffusion testing?
Agar diffusion tests are beneficial for assessing the cytotoxicity of elastomeric closures. In these tests, the agar layer acts as a cushion. The agar protects the cells from any mechanical damage and allows any leachable chemicals to diffuse from the product or packaging samples. The cells are then evaluated to determine the toxicity of the samples. Material extracts can also be assessed for cytotoxicity using the agar diffusion test by applying material extracts to a piece of filter paper.
What is in-vitro elution testing?
Elution tests are designed for evaluating extracts from plastic materials. Elution tests for cytotoxicity are beneficial for assessing high-density materials and evaluating dose-response in-vitro. Elution testing methods allow sample extraction at multiple times and under various temperature conditions.
What is in-vivo systemic injection testing for cytotoxicity?
A systemic injection is an injection into the circulatory system. Systemic injection testing determines the local biological responses of animals (mice) to plastic extracts injected into the bloodstream. Systemic injection testing and intracutaneous testing may be performed using the same extracts. Extracts are prepared depending on the heat resistance of the material being assessed. Thus, extracts are prepared at either 50°, 70°, or 121°C. Natural elastomers are tested in sodium chloride injection and vegetable oils only. Sample sizes for elastomer extract preparations are twenty-five centimeters squared worth of combined surface area per twenty milliliters of extract medium. Elastomers used for extracts must remain uncut. USP 88 provides additional details on extract preparations for intracutaneous testing.
Systemically injected mice are assessed immediately after injection and at 4, 24, 48, and 72 hours after injection. Each study uses ten mice. All mice injected with polymer extracts must show the same or less reactivity as controls injected with blanks to pass this examination.
What is in-vivo intracutaneous testing for cytotoxicity?
An intracutaneous injection is an injection between the layers of the skin. Intracutaneous testing determines the local biological responses of animals (rabbits or guinea pigs) to plastic extracts injected under the skin. Systemic injection testing and intracutaneous testing may be performed using the same extracts. Extracts are prepared depending on the heat resistance of the material being assessed. Thus, extracts are prepared at either 50°, 70°, or 121°C. Natural elastomers are tested in sodium chloride injection and vegetable oils only. USP 88 provides additional details on extract preparations for intracutaneous testing.
For each plastic sample, two animals are intracutaneously injected. After injection, the injection sites are assessed for evidence of any tissue reaction such as erythema, edema, and necrosis. All animals are observed at 24, 48, and 72 hours after injection for tissue reaction. The average erythema and edema scores for the control injection sites are also assessed at 24, 48, and 72 hours. Scoring systems and pass/fail criteria for this test can be found in USP 88.
Summary
Overall, many product-packaging systems use plastic materials known as elastomers. Elastomeric plastics are used in injectable products such as vials, bottles, prefilled syringes, flexible bags, and blow-fill-seal containers. Stoppers, cap liners, plungers, needle shields, tip caps, seal liners, and injection ports are all examples of injectable product components that utilize plastics. Any plastic with direct or transient contact with a pharmaceutical product or medical product formulation must pass certain regulatory requirements before being used as a device or packaging material. Safety tests for elastomeric plastics fall under two primary categories: package integrity testing (e.g., functionality, seal quality, and leak testing) and cytotoxicity testing (e.g., biological reactivity and physiochemical testing). Five elastomeric closure cytotoxicity tests are described in this article. Direct contact, agar diffusion, and elution tests are the benchtop assays. In contrast, the in-vivo assays are systemic injection and intracutaneous cytotoxicity tests. Only in-vitro (benchtop) testing will be necessary to evaluate elastomer cytotoxicity in nearly all circumstances. All in all, ensure you choose a contract manufacturing organization that can support you with appropriate cytotoxicity testing for your unique parenteral or injectable product needs.
MycoScience is a contract manufacturing organization specializing in sterile syringe and vial filling. MycoScience also offers Preservative Efficacy Testing, Cytotoxicity Testing, Bioburden Testing, Cleaning Validations, Microbial Aerosol Challenge Testing, Accelerated Aging, Microbiology Testing, EO Residual Testing, Bacterial Endotoxin Testing, Package Integrity Testing, Sterilization Validations & Environmental Monitoring services medical devices and allied industries. MycoScience is an ISO 13485 certified facility.
References
Draize JH, Woodward G, Calvery HO. Methods for the study of irritation and toxicity of substances applied topically to the skin and mucous membranes. The Journal of Pharmacology and Experimental Therapeutics. 1944;82:377–390.
Michael J. Akers. Sterile Drug Products Formulation, Packaging, Manufacture, and Quality. Drugs and the Pharmaceutical Sciences. Informa Healthcare. 2010.
United States Pharmacopeial Convention. <87> Biological Reactivity Tests, In Vitro. Rockville, MD, USA. 2021. (USPC <87>).
United States Pharmacopeial Convention. <88> Biological Reactivity Tests, In Vivo. Rockville, MD, USA. 2021. (USPC <88>).
United States Pharmacopeial Convention. <381> Elastomeric Components In Injectable Pharmaceutical Product Packaging/Delivery Systems (USPC <381>).
