Cytotoxicity Testing vs. Ethylene Oxide Residual Testing
What is cytotoxicity?
The “cyto” in cytotoxicity stands for cell. The “toxic” component of cytotoxicity refers to something that is poisonous. Thus, cytotoxicity refers to molecules and compounds that are poisonous to living cells. Cytotoxins are often chemical in nature but can also be from natural or biological sources.
What is ethylene oxide?
Ethylene oxide (EO) is a gas commonly used to chemically sterilize medical devices and products. The EO chemical sterilization process is used on materials that cannot withstand traditional heat and steam sterilization methods.
How does cytotoxicity relate to ethylene oxide?
Cytotoxicity refers to all molecules and compounds poisonous to living cells, whether these molecules come from artificial, natural, living microorganisms or inanimate sources. Bioavailable residual EO is cytotoxic. Two other EO residual gases, ethylene glycol (EG) and ethylene chlorohydrin (ECH), are also toxic at certain levels. While cytotoxicity testing evaluates the general cytotoxicity of all potential leachables and components of a medical device or product, EO residual testing specifically tests for EO and ECH to ensure medical products and devices sterilized with EO will not be toxic to patients upon use.
What are the differences between ethylene oxide residual testing and cytotoxicity testing?
The testing methods and metrics for cytotoxicity and EO residual testing have no similarities. This is because EO residual testing is specific to quantifying EO and ECH residuals from EO sterilized medical devices or products, whereas cytotoxicity generally measures the cytotoxicity of medical devices or products. When determining the amount and type of EO residuals in your medical device, two different methods are used for EO residual analysis. The two methods for EO residual evaluation are simulated-use extraction and exhaustive extraction. Evaluation of a device via either simulated-use or exhaustive extraction is sufficient to meet the ISO 10993-7 standards for EO residual testing. Evaluation of a medical device via both simulated-use and exhaustive extraction is not necessary.
Cytotoxicity testing evaluates the biological reactivity of mammalian cells and tissues to contact with elastomeric plastics and other polymeric materials that will come in direct or indirect patient contact during medical device or product use. 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. In-vitro methods of cytotoxicity testing include direct contact, agar diffusion, and elution testing. In-vivo methods of cytotoxicity testing include intracutaneous injection, systemic, and implantation testing. Most medical devices and products will only require in-vitro cytotoxicity testing. Reusable devices may require cytotoxicity testing for initial use and device use following recommended reprocessing. Cytotoxicity testing follows the methods outlined in USP 87 for in-vitro testing and USP 88 for in-vivo testing.
Why are both EO residual testing and cytotoxicity testing important?
Cytotoxicity testing is especially for medical products or devices that will be inserted into the human body. Suppose cytotoxins (such as leachable chemicals or bacterial endotoxins) exist on or within medical devices or products. In that case, the patient exposed will be at risk of fever, organ failure, cancer, and (in severe cases) death. Thus, cytotoxicity testing is an important quality control step for medical devices or products.
Regarding EO residual testing, EO sterilized materials vary in their ability to absorb, retain and release ethylene oxide (EO). If your device isn’t in contact with the patient, there is no need to perform EO residual testing. However, if your device is in contact with the patient, EO sterilized devices are placed into one or more of three exposure categories based on the duration of contact a medical device has with a patient. These categories are designed to protect patients against EO-related cellular toxicity that can cause varying degrees of illness and tissue damage. The categories of EO exposure are limited exposure (less than 24 hours), prolonged exposure (1 day to 30 days), and perpetual exposure (lifetime limit). Each category has specific limits (in milligrams) that must be met. You can find the specific EO and ECH residual limits for each exposure category here.
Summary
Overall, both cytotoxicity and EO residual testing are imperative for regulatory approval of a medical device or medical product. These tests ensure that medical devices and products are free of harmful toxins and are an important part of toxicity testing for product safety. When choosing a contract testing organization for your medical devices and products, ensure you find a company that suits your medical device or products unique needs.
Ethide Labs is a contract testing organization specializing in Cytotoxicity Testing and EO Residual Testing. Ethide Labs also offers Sterilization Validations, Microbiology Testing, Bacterial Endotoxin Testing, Bioburden Testing, Package Integrity Testing & Environmental Monitoring services for medical device companies and allied industries. Ethide is an ISO 13485 certified facility.
References
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>).
International Organization for Standardization. Biological evaluation of medical devices — Part 7: Ethylene oxide sterilization residuals. Geneva (Switzerland): ISO; 2008. (ISO 10993-7:2008).
