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Flashcards in Sterilization Deck (23):

Sterilization and sterility definitions

Sterilization- complete elimination of micro-organisms including bacterial spores (not prions)
Sterility- the absence of viable micro-organisms


Sterilization overview

Sterilization is an essential stage in the processing of products for parenteral administration, contact with broken skin, mucosal surfaces or internal organs, and the sterilization of microbiological materials, soiled dressings and other contaminated items


Terminal sterilization

Product is sterilized in its final container wherever possible
Wherever possible, appropriate additional treatment applied e.g. heating of the product in its final container
In all cases, the container and closure are required to maintain the sterility of the product throughout its shelf life
If terminal sterilization is not possible, filtration through a bacteria- retentive filter (aseptic processing) is used


BP methods of sterilization

Moist heat (steam sterilization)
Dry heat
Gamma or electron radiation
Ethylene oxide gas
Other methods can be used if they are appropriately validated


Physical, chemical and removal processes

Physical processes- elevated temperature (moist and dry heat), irradiation (gamma rays, high energy electrons)
Chemical processes- the application of a biocidal agent (glutaraldehyde, peracetic acid), reactive gas (ethylene oxide, LTSF, chlorine dioxide), gas plasma
Microbial removal processes- filtration


Choice of sterilization methods

Level of microbial contamination (bioburden)
Properties of the product to be sterilised: aqueous, oily solutions, emulsions, or dry powder device- metal, plastic, combination of materials, natural e.g. cotton or synthetic materials
Effect of method on product (physical, chemical)
Effect of method on product container/package (physical, chemical)
A suitable process has to be selected to ensure maximum microbial kill/removal with minimum product deterioration


Sterility assurance level

Inactivation of micro-organisms by any sterilization process follows an exponential law
There is always a finite possibility of one living cell surviving
The probability of microbial survival is determined by: the number, type, resistance properties and environmental conditions existing within the sterilizing process


SAL definition

SAL is the degree of assurance for a sterilizing process to render a population of products sterile
Determination of the probability of a non-sterile item being present within the product population


Moist heat disinfection

Moist heat disinfection: temperature below 100c
Pasteurisation: 63c/~30 min; 71c/15s
Tyndallisation- intermittent heating


Moist heat sterilization

Temperature of 100c and above
Steam under pressure (autoclaving); to attain high temperatures
Ultra-high temperature (UHT) 140c/4 s
The most reliable and widely used means of sterilisation


Moist heat sterilization- mechanisms of lethality

Antimicrobial activity- multiple effects
Denaturation of structural and functional proteins, nucleic acids and lipids
Coagulation of proteins and other components to cause cell death


Moist heat sterilization process

A three part process:
Heating up stage- articles to be treated are raised to appropriate sterilization temperature
Holding stage- sterilization process
Cooling down stage
Heating up and cooling down stages may contribute to the overall biocidal potential of the process


Drying or cooling stages

Dressings packs and other porous loads may become dampened and must be dried before removal from the chamber
Achieved by steam exhaust and application of a vacuum
After drying, atmospheric pressure within the chamber is restored by admission of sterile filtered air


Parametric release

The declaration that a product is sterile, based on records demonstrating that the process parameters were delivered within specified tolerances
The decision to release a load of processed devices is based on the results of physical measurements
Do not have to demonstrate that the product is sterile but that the physical parameters have been met


Dry saturated steam

Moist heat sterilization requires that steam must be dry and saturated
Saturated- steam is holding as much water as possible in the form of transparent vapour
Dry- it does not contain water droplets


Liquid and surfaces

Liquid- raise temperature of liquids within product containers to selected sterilization temperature
Surfaces- 80% of heat energy of steam is released in the form of latent heat when it contacts a cooler surface, this results in steam condensation and contraction, heat and moisture are imparted rapidly to articles being sterilized, dry porous loads are quickly penetrated by the steam


Superheated steam

Results from increase in temperature of dry saturated steam without increase in pressure, or from reduction of pressure at constant temperature
Degree of saturation of steam reduces, heat transfer will be similar to dry heat i.e. less effective sterilant
Transient superheating can be tolerated (max. acceptable level of 5c)


Wet steam

Results from decrease in temperature of dry saturated steam without decrease in pressure, of from increase at constant temperature
Dry products e.g. dressings become wetted/soaked preventing good penetration of steam into porous material


Moist heat sterilization problems

Air removal- important to remove air from the chamber because it impedes the penetration of steam
Steam purity- water contaminants can be carried over in steam and deposited onto the products- toxic effects and damage, determined by the quality of water
Cannot destroy bacterial endotoxins


Dry heat sterilization overview

Applications (quite limited in practice) restricted to powders, glassware, metal surgical instruments, non-aqueous thermostable liquids
Industrial application- sterilization of glass bottles filled aseptically
Destroys bacterial endotoxins


Dry heat sterilization methods of lethality

Lethal effects of dry heat are due largely to oxidative processes
Higher temperatures and longer periods are needed than for moist heat
Air is a less efficient conductor of heat than steam
Design- hot air oven, infrared conveyor oven, depyrogenation tunnels


Dry heat sterilization process

Dry heat sterilisation usually employs temperatures in the range 160-180c and requires exposure times of up to 2 hours depending upon the temperature employed


Dry heat sterilization advantages and disadvantages

Advantages: less expensive than moist heat sterilization, useful for moisture sensitive items, no corrosion, useful depyrogenation method (destruction of endotoxin)
Disadvantages: higher temperatures/longer cycle times