Ethylene Oxide Sterilization (EO) of Medical Devices

Principles, Process and Regulatory Relevance for Non-EU Manufacturers

Sterilization is a critical pillar of medical device safety and regulatory compliance worldwide. Among the available sterilization technologies, ethylene oxide (EO) sterilization — also referred to as ETO or EtO sterilization — remains one of the most widely used methods, particularly for complex and temperature-sensitive medical devices.

For manufacturers based outside the European Union, EO sterilization is often a key enabling technology for accessing the EU market under the Medical Device Regulation (MDR) and for meeting internationally harmonised ISO standards.

Sterilization is a critical pillar of medical device safety and regulatory compliance worldwide. Among the available sterilization technologies, ethylene oxide (EO) sterilization — also referred to as ETO or EtO sterilization — remains one of the most widely used methods, particularly for complex and temperature-sensitive medical devices.

For manufacturers based outside the European Union, EO sterilization is often a key enabling technology for accessing the EU market under the Medical Device Regulation (MDR) and for meeting internationally harmonised ISO standards.

How Does Ethylene Oxide Sterilization Work?

Ethylene oxide sterilization is a chemical sterilization process that uses ethylene oxide gas to inactivate microorganisms such as:

The gas disrupts the DNA and reproductive capability of microorganisms, achieving effective sterilization at relatively low temperatures, making the process suitable for sensitive materials and complex device designs.

Which Medical Devices Are Sterilized Using Ethylene Oxide?

Ethylene oxide sterilization is particularly suitable for devices that cannot tolerate high temperatures, moisture or ionizing radiation.

Typical examples include:

• complex and pre-assembled medical instruments
• catheters and multi-lumen tubing
• devices containing electronics or sensors
• stents and wound dressings
• single-use kits and surgical sets
• products made from polymer resins and plastics

Due to its excellent penetration capability, EO gas can pass through permeable packaging materials and reach all exposed surfaces — even in multilayer or intricately packaged products.

Ethylene Oxide Sterilization Process – Step by Step

A typical EO sterilization cycle consists of three main phases:

Advantages of Ethylene Oxide Sterilization

• Material-friendly: Low processing temperatures (typically 30–60 °C) protect heat-sensitive materials
• High penetration: Effective for complex geometries, long lumens and packaged products
• Broad material compatibility: Suitable for plastics, coated products, electronics and sensor-based devices

These advantages make EO sterilization a preferred option for many high-risk and technologically advanced medical devices.

Challenges and Limitations

Despite its benefits, EO sterilization presents specific challenges that manufacturers must manage carefully:

• Sterilant residues: EO and its by-products are volatile and toxic; adequate aeration is required to meet regulatory limits
• Long cycle times: Aeration can significantly extend overall processing time
• Regulatory scrutiny: Compliance with ISO standards (e.g. ISO 10993-7, ISO 11135) is mandatory, and processes must be validated

Validation of EO Sterilization Processes – ISO 11135

Validation of EO sterilization processes is performed according to ISO 11135. The Performance Qualification (PQ) phase is divided into:

• Microbiological Performance Qualification (MPQ)
• Physical Performance Qualification (PPQ)

Microbiological Performance Qualification (MPQ)

The MPQ demonstrates that the sterilization process consistently achieves a Sterility Assurance Level (SAL) of 10⁻⁶.

The most common validation approach is the overkill method (ISO 11135, Annex B), which uses biological indicators (BIs). Half-cycles and full cycles are performed to show that BIs are inactivated even under reduced exposure conditions.

Physical Performance Qualification (PPQ)

The PPQ confirms that all physical process parameters — such as EO concentration, temperature, pressure and humidity — remain within defined tolerances throughout the cycle.

ISO 11135 also describes alternative validation approaches (Annex A), which may be applicable depending on product and process characteristics.

EO Sterilization Compared to Other Methods

Compared to steam or radiation sterilization, EO offers greater flexibility and material compatibility. However, it requires:

• specialized facilities
• longer processing times
• experienced personnel
• robust residue control strategies

Selecting the appropriate sterilization method should always be based on product design, material compatibility, regulatory requirements and risk management.

Standards Update – ISO 10993-7 (EO Residues)

A key standards development relevant to EO sterilization is the update of ISO 10993-7, which defines acceptable limits for EO and ethylene chlorohydrin residues in medical devices.

• A revised draft was published in 2024
• The final version is expected in 2025

Key Update

The revised ISO 10993-7 introduces a standard reference body weight of 70 kg as the basis for residue limit calculations. This allows:

• improved transparency
• better alignment across patient populations
• more differentiated risk assessments

The exposure-category-specific limits (e.g. short-term vs. long-term use) remain unchanged, but a weight-based adjustment factor is now applied.

ISO 10993-7 continues to define:

• analytical methods for EO and ethylene chlorohydrin residues
• requirements for demonstrating compliance

For manufacturers and EO sterilization service providers, it is strongly recommended to monitor the final publication closely and update validation and risk management documentation accordingly.