Sterilization Flashcards
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 Filtration 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
Steaming
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
