1. VALIDATION OF MOIST HEAT STEILIZATION
JM Tech.
Do-Young Ahn
Moist Heat Sterilization

2. Moist Heat Sterilization
Definition
 Sterilization
“The act or process, physical or chemical, that destroys or eliminates all viable microbes including resistant bacterial spores from a fluid or a solid.”
Examples of sterilization methods are : steam treatment at 121℃, dry heat at 230℃, flushing with a sterilizing solution such as hydrogen peroxide (H2O2) or ozone (O3), irradiation, and filtration.
Sterility
“The reduction of anticipated levels of contamination in a load to the point where the probability of survival is less than 10-6.”
Moist Heat Sterilization

3. Moist Heat Sterilization
Definition
D-value
The time in minutes required for a one-log or 90% reduction of a specific microbial population under specified lethal conditions. For steam sterilization it is determined at a constant temperature
z-value
The number of degree of temperature change necessary to change the D-value by a factor of 10.
Z-value measures the rate of change in the D-value as a function of temperature.
Z=(T2-T1)/Log(D2/D1),
D값을 1/10로 단축시키는데 소요되는 온도상승값
Moist Heat Sterilization

4. Moist Heat Sterilization
Definition
F value(lethal rate, instantaneous Fo)
The F value is a measurement of sterilization effectiveness. F(T,z) is defined as the equivalent time at temperature T delivered to a container or unit of product for the purpose of sterilization, calculated using a specific value of z.
Fo value(accumulated Fo)
The term "Fo " is defined as the number of equivalent minutes of steam sterilization at temperature 121.1°C delivered to a container or unit of product calculated using a z-value of 10°C.
Fo =  10^((121-T)/z)*t
Moist Heat Sterilization

5. Moist Heat Sterilization
Methodology
Overkill Sterilization
Provides a minimum 12 log reduction of a resistant BI w/ a known D-value of not less than 1 minute.
Required minimal information on the bioburden
Bioburden/Bioindicator Sterilization
Provides a probability of survival of less than 1 in 106 for the bioburden as demonstrated using a resistant BI w/ a known D-value.
BI may not be inactivated
Requires information on the numbers and heat resistance of the BI.
Requires ongoing monitoring or control over bioburden.
Moist Heat Sterilization

6. Moist Heat Sterilization
Methodology
Bioburden Sterilization
Provides a probability of survival of less than 1 in 106 for the most resistance bioburden expected in the load.
Requires information on the numbers and heat resistance of the BI.
Requires ongoing monitoring or control over bioburden.
Moist Heat Sterilization

7. Moist Heat Sterilization
Sterilizer Cycle
Gravity Displacement
Difference of density
Density of air at 20℃ = 1.2 g/ℓ
Density of steam at 100℃ = 0.6 g/ℓ
Effectiveness of air elimination depends on the rate of steam supply
Air pocket : too rapidly
Diffusion into the steam : too slowly, more difficult to remove
Specially designed steam trap permitting the passage of large volume of air
Moist Heat Sterilization

8. Moist Heat Sterilization
Sterilizer Cycle
Prevacuum cycle
A more effective method
By means of a mechanical vacuum pump or a steam eductor
Vacuum as low as 15~20 mmHg, apply for 8~10 min.
Pulsing cycle
A series of alternating steam pulses followed by vacuum excursions
Air-steam mixture
Terminal sterilization of large volume parenterals
Air injection required to compensate the great expansion of air or nitrogen in the head space above the liquid
Well mixed chamber : fan, raining effect by external pump w/ cooling
Moist Heat Sterilization

9. Moist Heat Sterilization
Cycle Development
Consider factors into account
Nature of the load : porous materials, heat sensitivity of the products
Type of the sterilizer
Employed containers and closures
Heat stable product : overkill approach
Heat liable product : bioburden approach
Bioburden studies : number of microorganisms
D-value studies : only highly resistant spore formers,
BIER(biological indicator evaluator resistometer)
Inoculate the spore into the actual solutions
For solid materials, precut strips
Moist Heat Sterilization

10. Preparing for Validation
Temperature sensing devices :
 T type thermocouples(copper-constantan) encased in flexible sheaths
 Premium grades of wire having 0.1℃ accuracy
Temperature standards
 RTD traceable to the National Bureau of Standards , IPR, HTR
Calibration of thermocouples
At two temperatures : 0 ℃, 130 ℃
Correction factors
Stability : 0.03℃
Accuracy : 0.5℃
Moist Heat Sterilization

11. Preparing for Validation
Autoclave
Validation nozzle and adaptor
Data logger : digital output and multi-channel device
BIs or biological challenges
Loads
Moist Heat Sterilization

12. Moist Heat Sterilization
Validation Protocol
Protocol should include
Objectives of the validation
Responsibilities of validation personnel and operating department personnel
Identification and description of the sterilizer and its process control
Identification of SOPs :equipment
Calibration of instrument : SOPs and/or description
Identification and calibration of the temperature monitoring equipment
Moist Heat Sterilization

13. Moist Heat Sterilization
Validation Protocol
A description of the following studies
Bioburden determination studies(if applicable)
Empty chamber heat distribution studies
Container mapping studies(if applicable)
Loaded chamber heat penetration studies
Microbiological challenge studies
Evaluation of drug product cooling water(if applicable)
Integrity testing of vent filter
Acceptance criteria
References
Review and approval
Moist Heat Sterilization

14. Heat Distribution Studies
To demonstrate the temperature uniformity and stability of the sterilizing medium throughout the sterilizer
Conduct on both the empty and loaded chamber with max. and min. load configurations
Acceptance criteria : Less than ±1℃of the mean temperature
Conduct 3 runs to obtain consistent results
Distribution of the thermocouples : geometrical representatives, exhaust drain, adjacent to the control sensor
At least 10 probes, normally 15~20 probes
Temperature uniformity of the heat distribution studies may be influenced by
Type
Size
Design
Installation of the sterilizer
Moist Heat Sterilization

15. Heat Distribution Studies
At loaded chamber heat distribution test, the thermocouples should be positioned in the same locations used for empty chamber heat distribution
Avoid contacting solid surfaces
Do not place within any containers
Data should be obtained at regular intervals
Moist Heat Sterilization

16. Moist Heat Sterilization
Container Mapping
To determine the coolest point within the liquid filled container
Temperature mapping should be conducted on all the different container types, sizes and fill volume to be validated
The number of the thermocouples used depends on the container volume
Possible to use a single thermocouple at different positions,
and can be conducted in a smaller autoclave or retort
Penetration thermocouples should be positioned at the cold spot having lowest temperature or Fo
Container mapping studies can be conducted in a small autoclave or retort.
The temperature profile of the container should remain constant among different sterilizing chamber.
Moist Heat Sterilization

17. Heat Penetration Studies
To determine the coolest point(s) within the specified load and configuration, and to assure that these points be consistently exposed to sufficient heat lethality
Prior to conduct heat penetration studies, determine max. and min. load configurations
Probed container at the cold spot should be distributed uniformly throughout the load
Penetration thermocouple are positioned at points within the process equipment suspected to be the most difficult for steam heat penetration
Moist Heat Sterilization

18. Heat Penetration Studies
Lethal rate can be determined from the temperature data
by the following formula :
L = log-1(To-Tb)/z = 10^((To-Tb)/z)
A summation over time of the lethal rate at a series of temperature(accumulated lethality)
Fo =  10^((121-T)/z)*t
Regard to product stability
Moist Heat Sterilization

19. Microbial Challenge Studies
Biological challenges are employed during heat penetration studies in order to demonstrate the degree of process lethality provided by the sterilization cycle
Microorganism frequently utilized
Overkill : Bacillus stearothermophilus and Clostridium sporogenes
Bioburden : Calibrated BIs from environmental and process
isolates such as E. coli
Type of BI :
Spore strips or spore suspension into the suspending medium
Microbial challenge studies are conducted concurrently with the heat penetration studies
Moist Heat Sterilization

20. Moist Heat Sterilization
Validation Report
Common elements of all reports :
Identification of the task report by number
Reference to protocol
A brief summary of the range of operational conditions experienced and how they were controlled
A procedure for maintaining control within the approved range
A summary and analysis of the experimental results
A brief description of any deviation
Conclusion
Review and approval
Cycle development reports are not usually a part of the validation report
Moist Heat Sterilization

21. Maintenance of Validation
A routine calibration program for all instruments critical to the operation of the sterilizer and its support system
A preventative maintenance program including periodic operational rechecks and comparison to OQ record
Routine monitoring of bioburden and periodic BI challenges(optionally)
Operating records and equipment logs
Process and equipment change control procedures including review to establish whether additional validations are required
On-going validation
Moist Heat Sterilization

22. Moist Heat Sterilization
Controversial Issues
Incubation of the sterility test : 7 days vs. 14 days
USP provide information concerning critical parameters for Parameteric Release
Reduction extent and frequency of revalidation
Verification of D-value of BIs
Use of alternative to B. stearothermophilus as a BI
Moist Heat Sterilization