Guide to validation of terminal sterilization process of drugs (GUI-0074): Process validation, sterilization by moist heat 

Moist heat sterilization is widely used for aqueous-based products. It's not used in instances where it results in product/material or packaging degradation. You must fully evaluate and document any degradation cases.

On this page

• Product/material definition
• Sterilizing agent specifications
• Equipment qualification
• Temperature distribution studies
• Heat penetration studies
• Biological challenge reduction studies

Product/material definition

You should describe the:

• material and the packaging system to be sterilized (for example, size(s), fill volume or primary packaging)
• process challenge device (PCD)

Note: When process parameters are defined using a bioburden-based method, you must include an estimation of bioburden.

Sterilizing agent specifications

Your specification for a moist heat sterilization process must include, at a minimum:

• requirements for purity and quality of steam (saturated steam processes only)
• requirements for dryness, superheat, saturation and non-condensable gases (saturated steam processes only)
• contaminants (including from additives), which should not be at a level to cause contamination of product or equipment

Sterilization process definition

Specify the sterilization process you use. This should include descriptions of the following:

• autoclave(s) used for production sterilization, including manufacturer and model
• operating cycle and/or graphic presentation
• monitoring device, its location and interpretation of results (if used to verify delivery of a specified sterilization process)
• holding time and minimum and maximum temperatures (and their locations) measured during this time in an empty sterilizer chamber

The process definition should also include:

• the minimum cycle lethality achieved throughout the sterilization load
• process parameters and their tolerances
  • use both pressure and temperature to monitor the process
  • measure physical process parameters to confirm reproducibility
• the location of reference measuring point
• the minimum and maximum pressure in sterilizing chamber
• falling and rising pressure gradient and tolerances
• quality and purity of water/steam
• the maximum quantity of each contaminant present in any liquid, gas, steam admitted to sterilizer chamber for product configurations that are unsealed or where there's potential contact with the product formulation or product fluid path
• requirements for conditioning the product before sterilization, where applicable
• load configuration
• restrictions on size and mass of the load
• reference loads to be used to evaluate the effectiveness of the sterilization process
• if used, the location and acceptance criteria for biological indicators (BIs) and chemical indicators (CIs) (such as heat penetration and temperature distribution probes)

Note: Wrap your dry porous hard goods item to be sterilized (other than products in sealed containers) in a material that allows air to be removed and steam to penetrate. The material should also prevent re-contamination after sterilization.

All parts of the load should be in contact with the sterilizing agent at the required temperature for the required time. All loaded items should be dry when they're removed from the sterilizer. Visually inspect to confirm load dryness (where possible). May also use gravimetric analysis as a part of the sterilization process qualification and/or acceptance.

Equipment qualification

Your moist heat equipment specification should include, at a minimum:

• a description of materials of construction
• a description of control, monitoring and recording devices
• a description and validation status of software used to control/monitor the process
• the location, space and environment where the equipment is to be installed
• for saturated steam sterilization processes, the purity and quality of steam (especially any requirements for dryness, superheat, saturation and non-condensable gases)
• a description of any other gas or water used in the process and means by which they are delivered to the chamber

Examples of instruments that need calibration:

• timers
• thermocouples
• water level indicators
• flow meters for water/steam
• temperature recorders and sensors
• conductivity monitors for cooling water
• pressure sensors for jacket and chamber pressure
• thermometers, including reference thermometers used for calibration of thermocouples and those used for chamber temperature monitoring

Note: The position of the temperature probes used to control and/or record should be determined during the heat distribution and penetration studies. Where applicable, check these against a second independent temperature probe, located at the same position.

Temperature distribution studies

Temperature distribution studies help determine temperature variation throughout the sterilization chamber. Supported by a risk assessment, you may include an evaluation of both the empty chamber and the loaded chamber in these studies.

The extent of the temperature distribution studies should be appropriately justified and based on a risk management approach.

Perform:

• temperature distribution studies according to written procedures
  • use temperature-measuring sensors or probes that have been calibrated before and after use
• empty chamber temperature distribution runs during equipment qualification
  • determine the number of runs based on quality risk management principles
  • studies should demonstrate that the temperature uniformity throughout the empty chamber is within the temperature variation limits established in the validation protocol

Also:

• specify the requirements for temperature uniformity based on the type of sterilizer and specific processing parameters
• use multiple temperature probes in each test run
  • use simultaneous data recording to capture a reading of each individual probe at specified time intervals
  • this will allow you to determine the slowest and fastest heating zones in the chamber
  • document the location of each probe
  • place probes to show temperature distribution throughout the sterilizer chamber
• collate the data from similar condition runs as appropriate into a temperature profile for the chamber
• perform loaded chamber temperature distribution studies
  • use maximum and minimum chamber load configurations to represent various material configurations
  • place multiple temperature probes throughout the chamber, but not inside the units of the load (this will determine the effect of any defined loading pattern on the temperature distribution within the chamber)
  • perform sterilization cycle test runs using different container sizes
  • use the sterilization parameters specified for the normal production process
  • document the position of each temperature probe in each test run
  • determine and document the slowest heating point(s) or cold spot(s) in each run
  • repeat runs to establish whether, for a given load configuration, the location of the cold spot(s) is fixed or variable
    • determine the number of required runs using a quality risk management approach
  • develop and document a temperature distribution profile for each load configuration
• evaluate each test run performed
  • certify completed studies before beginning temperature penetration studies

Heat penetration studies

Heat penetration studies verify that the required temperature or heat history has been reached throughout the load when subjected to moist heat sterilization. These studies are conducted to ensure that the coolest unit within a pre-defined loading pattern (including minimum and maximum loads) will consistently be exposed to sufficient heat lethality (minimum F₀ value).

You should:

• perform heat penetration studies according to detailed written procedures
  • use temperature-sensing probes that are calibrated before and after use
  • ensure simultaneous data recording is available to capture a reading of each individual temperature probe within specified time intervals
  • this will allow you to determine the slowest and fastest heating units in the chamber
• allow for variables such as container size, design, material, viscosity of solution and fill volume in your validation protocol
  • fill the container to maximum fill volume with the slowest-to-heat solution for the specified cycle
• consider initial container temperature-mapping studies (depending on the container size)
• conduct heat penetration studies with the maximum and minimum loading configurations for each sterilization cycle
  • use sterilization parameters that do not exceed normal production cycles
• monitor heat delivered to the load, including the slowest to heat items, if these are present
  • use this data to evaluate the achievement of the minimum lethality (F₀ value) requirements
• perform replicate runs to verify that the desired minimum process F₀ value can be achieved consistently throughout the load
  • determine the number of required runs using a quality risk management approach
  • the process is considered acceptable once such consistency in the achievement of minimum lethality has been adequately established

Note: For concepts on moist heat sterilization, consult:

• ISO 17665 Sterilization of health care products — Moist heat — Part 1: Requirements for the development, validation and routine control of a sterilization process for medical devices

Biological challenge reduction studies

Perform biological challenge reduction studies, when applicable (described in Phase 2, process performance qualification).

Note: You may run the biological challenge along with distribution studies and/or penetration studies.