Dry Heat Depyrogenation vs. Sterilization For Sterile Products
What Are sterilization and Depyrogenation?
Sterilization and depyrogenation keep patients safe from toxins and microbial illnesses when therapies or devices are consumed or used. Dry heat sterilization and depyrogenation are common for products that aren’t sensitive to heat. Depyrogenation is less common than sterilization because depyrogenation is an endotoxin removal method. Endotoxins aren’t as ubiquitous as bacteria, viruses, yeasts, and molds. Sterilization is any process that removes, kills, or deactivates all forms of life. Under the strictest definition of sterility, an item or product is sterile when there is the complete absence of viable microorganisms (bacteria, yeasts, viruses, and molds). For regulatory purposes, sterility is defined by acceptance criteria based on calculated contamination probability. An acceptable level of contamination risk for most items is the probability of a single contaminated product out of a million manufactured products. However, sterility criteria may be more stringent or lax depending upon the intended use of the medical device or product. Sterile products that undergo sterilization are often chemical, heat, or filter sterilized. Sterilization kills any microorganisms products collect during manufacturing. For chemical and heat sterilization, sterilization occurs after the product is placed in its final packaging. The product is often filtered and then aseptically filled into a sterile container for sterilization by filtration.
why is depyrogenation needed for sterile products?
Parenteral products must be sterile and pyrogen-free. Even if a product is sterile, it can still contain pyrogens. As mentioned above, depyrogenation is an endotoxin removal method that removes pyrogens. The most prevalent and problematic pyrogens are the bacterial endotoxins found in the outer cell walls of gram-negative bacteria. Thus, depyrogenation is a process that will either destroy or remove bacterial endotoxins. Products can accumulate pyrogens from raw materials or other parts of the manufacturing process. The best pyrogen removal or destruction processes are product-dependent. Standard depyrogenation methods are dry heat, rinsing, and filtration.
What are pyrogens, endotoxins, and lipopolysaccharide (LPS)?
Pyrogens are molecules or substances that cause a feverous reaction when they enter the human body. Endotoxins are the most common type of pyrogen. Endotoxins come from the cell walls of gram-negative bacteria. The endotoxins themselves are molecules with both fat components and complex sugar components. The presence of fat and sugar components is why endotoxins are also known in scientific literature as lipopolysaccharides (LPS). LPS is the biologically active portion of an endotoxin. In other words, LPS is the part of the endotoxin that triggers the innate immune system and causes illness in humans. Parenteral products and devices are contaminated with endotoxin through Gram-negative bacterial cells or cell wall fragments containing LPS. Lipopolysaccharide’s structure allows it to stick to hydrophobic (water-repellant) and hydrophilic (water-loving) surfaces. Thus, LPS components easily attach to molecules and proteins in solutions or material surfaces, causing endotoxin contamination. LPS also sticks to itself to form LPS chains known as aggregates. LPS can only be eliminated using endotoxin removal methods like depyrogenation.
What is dry heat sterilization?
Dry heat sterilization is a heat-based method that kills microorganisms by denaturing proteins within the cells at 170◦C or higher temperatures. More information on dry heat sterilization can be found in THIS article. Curious about dry heat vs. steam sterilization? Find out about dry heat and steam sterilization HERE.
What is depyrogenation by dry heat?
Dry heat depyrogenation is an endotoxin removal method that destroys endotoxins through exposure to high temperatures of 250◦C or above.
Should you use dry heat sterilization or dry heat depyrogenation for your sterile product?
Many sterilization techniques also provide depyrogenation. However, depyrogenation via dry heat requires special conditions compared to traditional dry heat sterilization techniques. Indeed, endotoxins require additional heat to be inactivated compared to microbes alone.
While materials sterilized with dry heat must be able to withstand temperatures of 170◦C or greater, products materials must be able to withstand high 250◦C or above temperatures without losing functionality for dry heat depyrogenation. Products that can withstand heat levels for steam sterilization (~121-132◦C) and humidity are the cheapest to process with an autoclave. However, temperature-sensitive materials that cannot withstand high heat, or are humidity sensitive, should be sterilized with radiation or ethylene oxide. If products are biologics, protein therapies, or other drugs that have components sensitive to radiation damage or ethylene oxide toxicity, sterile filtration should be used for sterilization and depyrogenation.
What are the similarities and differences between dry heat sterilization and depyrogenation processes?
The method for dry heat sterilization and depyrogenation is the same, except that temperatures of 250◦C or above must be used for depyrogenation. In contrast, dry heat sterilization alone can be performed at temperatures as low as 170◦C.
Summary
Medical devices, products, and therapies must be sterile and pyrogen-free. Sterilization is any process that removes, kills, or deactivates microbes, whereas depyrogenation is a process that removes pyrogens. The most prevalent and problematic pyrogens are the bacterial endotoxins found in the outer cell walls of gram-negative bacteria. Dry heat sterilization is a heat-based method that kills microorganisms by denaturing proteins within the cells at 170◦C or higher temperatures. Dry heat depyrogenation is the process of destroying endotoxins through exposure to high temperatures of 250◦C or above. Not all sterile products can withstand temperatures of 170◦C or 250◦C. Thus, alternative sterilization methods such as steam, ethylene oxide, radiation, and filtration may be needed if dry heat methods are too extreme for product materials. All in all, ensure you choose a contract testing organization that can provide appropriate sterility testing, bacterial endotoxin testing, and depyrogenation for your product needs.
Ethide Labs is a contract testing organization specializing in Sterility Testing and Sterilization Validations. Ethide Labs also offers Microbiology Testing, Bioburden Testing, EO Residual Testing, Bacterial Endotoxin Testing, Cytotoxicity Testing, Environmental Monitoring & Package Integrity Testing services for medical device companies and allied industries. Ethide is an ISO 13485 certified facility.
References
Review: Infection, fever, and exogenous and endogenous pyrogens: some concepts have changed. Innate Immunity. August 1, 2004.
Galanos C. and Freudenberg M. A. Bacterial endotoxins: biological properties and mechanisms of action. Mediators of Inflammation. 1993; 2(7): S11–S16.
International Organization for Standardization. Sterilization of health care products- Moist heat- Part 1: Requirements for the development, validation, and routine control of a sterilization process for medical devices. Geneva (Switzerland): ISO; 2006. (ISO 17665-1:2006/(R)2016).
Michael J. Akers. Sterile Drug Products Formulation, Packaging, Manufacture, and Quality. Drugs and the Pharmaceutical Sciences. Informa Healthcare. 2010.
United States Pharmacopeial Convention. <85> Bacterial Endotoxins Test. Rockville, MD, USA. 2021. (USPC <85>).
United States Pharmacopeial Convention. <1115> Bioburden Control of Non-Sterile Drug Substances and Products. Rockville, MD, USA. 2021. (USPC <1115>).
United States Pharmacopeial Convention. <1116> Microbiological Control & Monitoring of Aseptic Processing Environments. Rockville, MD, USA. 2021. (USPC <1116>).
United States Pharmacopeial Convention. <1211> Sterility Assurance. Rockville, MD, USA. 2021. (USPC <1211>).
United States Pharmacopeial Convention. <1228.1> Dry Heat Depyrogenation. Rockville, MD, USA. 2021. (USPC <1228.1>).
