"terminal sterilization basics of eo"
TRANSCRIPT
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Topics
• How does EO sterilize• Basic factors affecting sterilization• Calculating D value• Biological Indicators• An EO Cycle• Cycle Validation• EO Residues• Product Release
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Governing Standard• ANSI/AAMI/ISO 11135: Medical Devices –
Validation and routine control of ethylene oxide sterilization.
• www.aami.org
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How Does EO Sterilize?
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EO as a Sterilant
EO is the simplest epoxy• Boiling point 10.4°C (50.7°F)• Extremely reactive• Kills by alkylation
Irreversibly binds to key molecules in cellDNAProteins (enzymes)
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EO as a Sterilant
Molecules no longer function Cell no longer reproduces Cell dies
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Basic Factors Affecting EO Sterilization
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Four Basic Factors to Microbial Kill
•EO concentration•Water Vapor (Humidity)•Temperature•Time
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EO Concentration
•Commonly 400 and 700 mg/l •As EO concentration increases at a
given temp and RH, ▫microbial inactivation (kill) rate
increases
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EO Concentration
•Killing concentration required at the site where the microbes (BI’s) are located
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Water Vapor (Humidity)
•Required for EO to react with the critical cell molecules
Generally measured as Relative Humidity
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Temperature
•Kill rate increases with temperature▫D-value decreases (time) with
temperature▫Exponential function
•For each 10°C (18°F) rise in temperature, the spore inactivation rate will generally double
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Time
•Amount of kill increases with exposure (EO gas dwell) time
•90 percent of surviving microbes are killed for each D-value time in gas dwell
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D-Value
•Determined to prove predictable logarithmic death kinetics of challenge microorganisms (BIs) or natural bioburden
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D-Value
•“Decimal” Reduction Time - Measure of the biological organism’s resistance to the sterilant
•Time in minutes necessary to reduce (kill) a microbial population by one logarithm or 90%
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A Simple D-Value Calculation
TimeLog of Starting Population – Log of Final
Population
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Example•1,000,000 or 106 spores. (the Log = 6)•20 minute gas dwell•Result is 10,000 or 104 spores
(the Log = 4)
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Time = 20 minutesLog of Starting Population (which equals 6) – Log of Final Population
(which equals 4)
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20 minutes6 – 4
Thus: D-Value is 20 divided by 2 = 10 minutes
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What does that mean?
•It takes 10 minutes to go from:▫1,000,000 to 100,000▫ or 10,000 to 1,000▫ or 10 to 1▫ Etc.
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Biological Indicators
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Biological Indicators• In EO sterilization,
we use a paper strip impregnated with about a million spores . The strip is in a gas-permeable, bacteria-impermeable glassine envelope
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Biological Indicators (BIs)
•More difficult to kill than natural occurring bioburden (microrganisms in or on product)
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Biological Indicators (BIs)
•Traditionally, >106 spores of an organism (i.e., Bacillus atrophaeus) highly resistant to EO process
Spores
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Bacillus???
•The name of the bacterium is commonly Bacillus subtilis or B. subtilis.
• It has been renamed and is officially B. atrophaeus.
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Biological Indicators (BIs)
•Provided in various forms for industrial applications:▫Placed in product to represent
most resistant location in product
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Examples of Biological Indicators
SCBI Disc Strip SCBI
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Placing the BI: The BI is positioned in the
Most Difficult Location for gas to reach
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Testing EO-exposed BIs
•The BI strip or disc is planted into a test tube containing Tryptic Soy Broth (TSB).
•The strips are incubated at 30-35oC for seven days (USP).
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A Positive
Orange pellicle
Cloudy
Sediment
TSA Agar(orange)
Tyrosine Agar (black)
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The EO Cycle
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Conventional Cycle•Three steps▫Preconditioning▫Sterilization ▫Aeration
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Preconditioning•First “processing” step of EO
sterilization.•Ensures the load is always
processed at roughly the same temperature and humidity upon entry to the chamber.
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Preconditioning
•Heat and Humidity Introduced to Load
•Air circulated to assist heat/humidity transfer
•Generally 18-24 hrs
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Chamber
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EO Sterilization Cycle
Generic 100 Percent Cycle
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0 100 200 300 400 500 600 700
Time from Cycle Start (minutes)
Pres
sure
(inH
gA)
Initial Vacuum
Leak Test
Humidification
Humidity Dwell
Gas Inbleed
Gas Dwell
After Vacuum
Gas Wash
Final Release
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Cycle Validation
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•Rigorous microbiological and physical testing
•Beyond that used in routine monitoring for either:• Conventional• Parametric
Cycle Validation
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• Conventional Cycle Run 3 Half Cycles with parameters established during Cycle Development Culture BIs (2 to 7 days)
Run minimum 1 Full Cycle to evaluate functionality and residuals
Cycle Validation
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•Conventional Cycle (continued)▫Aeration Requirements
Develop dissipation curve to establish release time
Aerate long enough to assure safe residuals typically around 2 days on average
Cycle Validation
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Conventional Cycle (continued)• Residual allowable limits are based on
application of product ISO 10993-7 Qualify release time based on three (3) separate lots.• May be satisfied with first two routine runs with end-point residual testing (to supplement dissipation curve)
Cycle Validation
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Parametric ReleaseRelease on parameters, not BIAdded parameters; Load temp prior to Precon Load temp at end of Precon Chamber RH during humidity Chamber EO during dwell Load temp during dwell
Cycle Validation
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Parametric ReleaseBI Requirements NONE
Cycle Validation
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Critical step in overall validation • Periodic (typically annual)
requalification studies designed to detect inadvertant process changes
• Recommended upon introduction of new or significant changes in: Product Process Packaging Equipment
Revalidation
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•Options:
▫Perform one (1) micro PQ run in each qualified chamber
Revalidation
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•Options
▫Paper Revalidation: Documented evaluation of process to verify no process shifts throughout year. May be used as a tool, however not
recommended for continuous replacement of physical requalification.
Revalidation
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AERATION
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Aeration (Degassing)
•Last “processing” step.▫Aeration Room physically similar to
Preconditioning, but with no “Humidity”•Two methods of Aeration available▫Heated▫Ambient
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Aeration (Degassing)
Heated Aeration•Heat Introduced to Load▫assist in degassing process
•Typically 2 days on average for Heated Aeration
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Aeration (Degassing)
Ambient Aeration•generally has much longer minimum
time requirements
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EO Sterilant Residues
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EO Sterilant Residues
•What is a sterilant residue?•Why do we need to test?•Who tells us we have to test?•How do we test for these residues?
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What is a Sterilant Residue?
Sterilant residues are compounds that remain on product after ethylene oxide sterilization.
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Residues - What are They?
•Ethylene Oxide
•Ethylene Chlorohydrin - Formed when EO reacts with chlorine or chloride ions. Chlorine may come from salt or bleach.
•Ethylene Glycol - Formed when EO reacts with water.
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Why Test?
•Patient safety.
•Regulatory limits.
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Who Requires Testing?
•FR, Volume 43, No. 122- June 23, 1978 (FDA)
•ANSI/AAMI/ISO 10993-7
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Factors Affecting Levels of EO
Residual amount depends on:▫Product materials▫Chamber gas concentration▫Gas dwell time▫Aeration conditions and length of aeration time
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Product Release
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Product Release
•Before or after aeration BI’s are pulled from load and sent to lab for testing (7 day test)
• If Parametric Release has been validated, load can be released immediately after aeration. (No BI’s required)