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Cold Sterilisation
| Question | Answer |
|---|---|
| What are the 2 main gaseous sterilsing agents? How are they distinguished? | Ethylene Oxide and and Hydrogen peroxide Distinguished by their antimicrobial action (ethylene oxide is an alkylating agent, hydrogen peroxide is an oxidising agent) |
| Outline ethylene oxide | Alkylating agent that interacts with amino, sulfhydryl and hydroxyl groups to cause cytotoxic, carnigenic and mutagenic effects. Simple cyclic ester, colourless gas, highly flammable and explosive when mixed with air. |
| What are the toxicity concers with ethylene oxide? | Non-selective in its action so equally toxic to the operator as to the bioburden. Contact toxicity = oedeme, erytheme, skin eruptions, allergic reactions Vapour toxicity = eye/nose irritation, nausea, dizziness Very wide spectrum of activity |
| What is ethylene oxide used for? | Sterilise thermolabile equipment: plastics, lensed equipment, electrical and rubber Medicaments: thermolabile solids. Gas cannot penetrate the product, so just sterilises the surface |
| As outlined in the Bp, what is gas sterilisation used for? | Gas sterilisation of surfaces used for primary packaging materials, equipment and some pharmaceuticals. Gas and moisture penetration is confirmed, then the gas is removed so that any residues or related by products are below conc'n to avoid toxic effect |
| How does EO concentration influence efficiency? | Within limiting conc'n, double the conc'n doubles rate of inactivation Conc'n less than 300mg/l are insufficient to achieve sterility within a reasonable time In practice con'c range 500-800mg/k Con'c and temp are interrelated |
| How does temperature influence sterilisation efficiency for EO? | Under constant condition and within conc'n range, EO follows first order kinetics Rate of inactivation doubles every 10 degree increase Upper limits of temp are less important, ethylene oxide is used for cold sterilisation |
| How does humidity influence Eo sterility efficiency? | EO not effective against dehyrated MO's in a dry environment A surface film of water would promote contact by dissolving EO to form a concentrated solution Ideal humidity level is 33% |
| How is the aeration time affected? | Composition, thickness, design configuration, weight of device and wrapping material EO conc'n and time of sterilisation process Rate and pattern of airflow Intended use of the device |
| How is the process of EO sterilisation monitored? | Specialised equipment for monitoring temparture, humidity and gas conc'n during validation and normal operations. How effective sterilisation is depends on gas conc'n, temp, humidity, exposure time load configuration, characteristic of product and packing |
| How are biological indicators used in EO sterilisation process monitoring? | Used for all gas sterilisation, both for validation and normal operations. Spores used are bacillus subtilis. Placed at locations within the product where sterilisation is hardest to achieve. |
| How else is the process of Eo sterilisation monitored? | Occupational health and safety (incident rate, supply of PPE, signage etc) Sample of each batch tested for sterility before batch release. |
| Outline vaporised hydrogen peroxide | Oxidsing agent - reacts with lipids, proteins and nucleic acids to form high reactive hydroxyl radicals Sterilant produced by vapourising a 35% solution of HP into a carrier of warm dry air Sterilisation temp is 35-40C, HP 10mg/L |
| What is HP used for? Are there any toxicity concerns? | Used for sterilising endoscopes, dental sterilisers, surface disinfection of isolators Direct contact toxicity is low: temporary irritation |
| What are the key differences between EO and HP? | HP is much less toxic compared to EO and has more uses. |
| What is ionising radiation sterilisation? | Using gamma rays, Xrays or accelerated electrons to achieve sterilisation. Doesn't include UV light which is low energy, non-ionising radiation and has poor penetrating power. |
| What are properties/advantages of ionising radiation? | Kills all types of MO's, has enough energy to penetrate into solids and liquids (Stronger than gases) Doesn't heat or wet materials significantly |
| How does ionising radiation achieve sterilisation? | Exposure of the product to either gamma rays from isotopic source, a beam of electrons produced by an electron accelerator, or X rays from bombarding product with energised electrons. |
| What types of sterilisation can IR be used for? | Terminal sterilisation of finished dosage forms, microbial inactivation of tissues/cells, sterilisation of materials/containers to be used in aseptic processing. Low energy electrons can be used to sterilise surfaces of materials entering isolators. |
| How is IR used in practice? | Sterilise: plastic syringes and catheters, hypodermic needles and scalpel blades, adhesive dressings, single application capsules of eye ointments and catgut, polyethylene containers, aluminium foil and plastic film packaging materials, pharm/bio products |
| What is the mechanism of biocidal action for IR sterilisation? | Has 3 stages: ionisation, radical formation, biochemical changes. Causes 2 types of DNA damage: breaks in both or one strand of DNA, lesions in the nitrogenous bases. |
| What is a Gray? | unit of dose defined as 1 joule of energy absorbed per kg of material irradiated. |
| What is the dose used in terminal sterilisation for IR? | 25 kGy Other doses can be used but they must have demonstrated that the dose is adequate and reproducible under established operating tolerances. Procedures and precautions in place must achieve a SAL of 10-6 or better. |
| What are the sensitivities of MO's to IR? | Vegetative bacteria : sensitive 0.5-10 kGy Moulds and yeats: mod sensitive 4-30kGy Bacterial spores: resistant 10-50 kGy Most viruses: resistant 10-40 kGy Bacillus spores: highly resistant 35-80kGy |
| What factors influence IR suspecitiblity? | Oxygen: resitance increases 2-5 times in anoxic conditions Temp: increases reduce D values Organic substrates: have a protective ffect where they shield the MO and absorb radiation, reducing efficacy Chemical agents that remove free radical scavengers |
| How is the process controlled for IR sterilisation? | Radiation absorbed by the product is monitored by established dosimetry procedures independent of dose rate. Calibrated against a standard source at a reference radiation plant every 12 months Biological indicators and Ocuu health and safety |
Created by:
LDM
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