Sterilization Lecture Notes (2023/2024) PDF

Pharm D Program (2023/2024) 1 October 2024 www.su.edu.eg 1  Pharm PharmDDProgram Program (2024/2025) (2023/2024) (PM 502)...

Pharm D Program (2023/2024) 1 October 2024 www.su.edu.eg 1  Pharm PharmDDProgram Program (2024/2025) (2023/2024) (PM 502) Lecture No. (2) Sterilization-2 By Professor Yasser El Mohammadi 1 October 2024 www.su.edu.eg 2  Pharm PharmDDProgram Program (2024/2025) (2023/2024) Lecture’s Aim To allow the student to know the most important details about moist heat sterilization and gas sterilization including the used equipment in both processes. 1 October 2024 www.su.edu.eg 3  Pharm PharmDDProgram Program (2024/2025) (2023/2024) Lecture’s Competencies To enable the student to discover and decide which items are to be best sterilized by moist heat & by gas sterilization and the advantages of these two methods. 1 October 2024 www.su.edu.eg 4  Pharm PharmDDProgram Program (2024/2025) (2023/2024) Lecture’s Contents - Moist Heat Sterilization - Methods for moist heat sterilization I) At normal pressure (at or below 100oC) II) At high pressure (above 100oC) - Types of autoclaves II- COLD STERILIZATION A- GASEOUS STERILIZATION - Properties (& disadvantages) of ethylene oxide - Sterilizer design and operation - Formaldehyde sterilization 1 October 2024 www.su.edu.eg 5  2. Moist Heat Sterilization Water is an excellent medium for heat transfer but steam is much more better. At normal atmospheric pressure, 1 gm of water requires 100 calories to raise its temp from 1oC to 100oC, these calories are called sensible heat. Each gram also requires 560 calories to convert it from water at 100oC to steam at 100oC, these calories are called latent heat.  Methods for moist heat sterilization I) At normal pressure (at or below 100oC) For substances damaged by heat over 100oC a) Pasteurization: (not used in sterilization) First used by Louis Pasteur to kill Acetobacter and Lactobacillus (non spore forming bacteria) to prevent spoilage of wine. Later used to kill milk pathogens such as T.B., Brucella, Salmonella, poliovirus, etc… Pasteurization only improves the keeping quality of milk and at the same time maintains its nutritive quality. It is a type of disinfection or preservation, carried out in 2 ways: 1- Holding process: heating at 62oC for 30 min. then cooling to 7oC. 2- Flash process: heating at 72oC for 15 sec. or 82oC for few sec. then rapid cooling to 4oC. Public Health\milk1.flv Public Health\milk2.flv  UHT Milk Production.flv UHT plate sterilizer b) Sterilization of vaccines: By heating at a temp. which just kills the m.o. but does not affect its antigenicity. Cholera vaccine is sterilized by heating at 56oC for one hour, plague vaccine at 55oC for 15 min & Staphylococcus autogenous vaccine at 62oC for 15 min. c) Sterilization by heating with bactericide: This method involves heating at 100oC for 30 min in the presence of a bactericide, which should be non toxic, non volatile, stable, and compatible with other ingredients e.g. phenyl mercuric nitrate (0.002%), benzalkonium chloride (0.01%) or chlorocresol 0.2%. Basically, it is a type of chemical sterilization in which heating enhances the sporicidal activity of the bactericide. Disadvantages of this method: 1- Not used for intrathecal, intracisternal or intravenous injections with volume exceeding 15 ml (may cause toxicity). 2- Not used for oily injections (oil reduces the activity of most chemicals as they are water soluble). 3- The bactericide remains in the final preparation.  Pressure - Temperature Curve Water boils at 100oC at normal atmospheric pressure & in order to obtain moist heat (steam) over 100oC, water must boil under pressure. Heating water in a closed vessel (autoclave) will increase the pressure inside due to the generated steam and so the boiling temp. will increase and saturated steam is formed (all points on the Boiling point curve  boundary phase where steam & water are in equilibrium. It condenses easily & is a source of heat & moisture (moist heat). Saturated steam is either: a) wet steam (supersaturated steam): carry suspended water droplets which may cause excessive wetting of the sterilized material. b) dry steam: free from water droplets. The killing potential of wet saturated steam is the same as that of dry saturated steam at the same temp. At one atmospheric gauge, water boils at 121oC producing saturated steam at 121oC. When water is finished and heating is continued i.e. temp increases while pressure remains almost constant, saturated steam is converted into superheated steam (all points above the boundary). It has a temp. higher while pressure remains almost constant, saturated steam is converted into superheated steam (all points above the boundary). It has a temp. higher than that supposed at a specified pressure & it never condenses except when its temp is much reduced. Superheated steam is not suitable for moist heat sterilization as it acts only as a source of heat but not a source of moisture (dry heat). Advantages of using saturated steam in sterilization Depends on the fact that upon contact between saturated steam and cooler surface condensation occurs. 1) Condensation of steam results in release of large amount of latent heat which rapidly raises the temp. of the article to be sterilized. 2) Rapid heating-up so less damaging to objects than in dry heat. 3) Condensation of steam results in contraction of volume and so more steam comes in contact. 4) Condensation of steam results in moisture which requires low “E” & hence lower temp. & shorter time. 5) High penetration power. 6) Gives uniform temp. II) At high pressure (above 100oC) To obtain temp over 100oC, water must boil under pressure, where temp. is directly proportional to the pressure. Sterilization by moist heat usually involves the use of steam at temp. 115-134oC. Pressure only raises the boiling point of water but plays no role in the killing process.  Autoclave Large pressure cooker with controls for temp., pressure, air and cooling. Used for large scale pharmacy and in hospitals. - Suitable for thermostable aqueous injections in final sealed containers (ampoules or vials) and eye drops, surgical dressings and microbiological media. - Not suitable for oils and powders nor glass as repeated autoclaving causes its damage. In emergency it could be used in sterilization of glass. However, empty closed ampoules cannot be sterilized by autoclaving as water does not touch the inner surface. Main design features of autoclave Autoclave operating.flv  Types of autoclaves 1- Portable autoclave (bench autoclave) The steam is generated inside the autoclave, so steam is always wet. Pressure resistant metal or stainless steel. May be vertical or horizontal. May be double walled (steel jacketed). Heated electrically. Used for small scale sterilization in laboratories and for sterilization of instruments and utensils...\CONTROL.AVI 2- Stationary autoclave (large sterilizer) Large, horizontal vessel with complicated design, having the steam generated from a distant boiler as dry saturated steam. Usually surrounded by a steam-jacket. Used for routine hospital or industrial sterilization.  Types of large sterilizers 1- Dressings (porous loads) sterilizers Generally operated at a min. temp. of 134oC, and are supplied with a vacuum pump to remove air completely at the beginning and steam at the end of the process, to withdraw the load dry. 2- Bottled fluids sterilizers Generally operated at 121oC. They are supplied with a device for spraying cold water to cool down the load, or better by introducing filtered compressed air otherwise it may require very long time to cool. Small sealed containers (e.g. ampoules) must be aqueous (not oily) & must not be completely filled to allow generation of steam without cracking since steam cannot penetrate to the inside of the ampoules. Dressing sterilizer  Advantages of jacketed autoclave 1- Rapid in operation as steam is stored in the jacket. 2- More economic as steam is trapped in the jacket and not allowed to escape into the atmosphere. 3- Load comes out dry as the inner surface is always warm.  Why air is removed from the autoclave? 1- It reduces the penetration of steam especially within dressings. 2- It causes superheating in stationary autoclaves. 3- In temp. controlled autoclaves, explosion may occur. 4- In pressure controlled autoclaves, the temp. of air-steam mixture may be lower than expected because air holds lower amount of specific heat than steam so the sterilizing temp. may not be reached. 3- In presence of air, more heat is required to reach the same temp. i.e. less economic.  II- COLD STERILIZATION A- GASEOUS STERILIZATION Specific alkylating agents such as the chemically reactive gases ethylene oxide, b-propiolactone, propylene oxide and formaldehyde possess broad spectrum biocidal & sporicidal activity. Ethylene oxide is considered as an alternative to radiation sterilization in the commercial production of disposable medical devices. This technique does not however offer the same degree of sterility assurance as heat methods and is generally reserved for thermolabile items. The mode of action of ethylene oxide and formaldehyde is assumed to be through the alkylation of sulfhydryl, amino, hydroxyl and carboxyl groups of proteins and imino groups of nucleic acids. Suitable for - Plastics (syringes, containers) - All antibiotics and hormones (except if they react with ethylene oxide) - Reusable medical & surgical instruments - Certain medical diagnostics - Surgical dressings and sutures - Surface sterilization of powders Not suitable for - Substances which react with ethylene oxide such as serum, vaccines, and aqueous solutions. - Many oily preparations (not penetrate & need humidity). - Preparations in sealed glass or metal containers. Properties (& disadvantages) of ethylene oxide: 1- Gas at normal atmospheric pressure (boiling point 10.5oC) 2- Inflammable and explosive when mixed with air in conc. exceeding 3.5% v/v. 3- Either mixed as 10% with CO2 (carboxide), and kept in heavy cylinders & is cheap, or mixed as 12% with Freon (cryoxide), and kept in light cylinders but is expensive. 4- Toxic as ammonia. 5- Mutagenic and carcinogenic. It is important, therefore, that ethylene oxide sterilization is carried out in accordance with a strict working protocol and that the environment gas levels is monitored to ensure the safety of operators. 6- Relatively slow action (exposure time:1-4 hours).  Factors affecting efficacy of ethylene oxide 1- Conc.: 800 - 1200 mg/liter of the sterilizer volume. 2- Temp: 45 - 63oC. 3- Relative humidity: 30-60%, activity decreases below 30% due to the decrease in alkylating activity, and above 60% due to formation of ethylene glycol with water which is completely inactive. 4- Penetration: does not penetrate glass, metals and crystals, so it is not used for the sterilization of crystals required to dissolve in the body except if they are crystallized aseptically from sterile solutions. However, it could be used for surface sterilization of plastics and it penetrates fabrics (dressing) and paper (packing material must be air, steam and gas permeable). Sterilizer design and operation It consists of: 1- Leak –proof and explosion-proof steel chamber (gas autoclave), 100-300 liters capacity, surrounded by hot water jacket to regulate temp. 2- Vacuum pump to evacuate air at the beginning and gas mixture after sterilization. 3- Source of steam for humidification? - Sterilized articles must be kept for a time in good ventilated area to remove the adsorbed ethylene oxide since it is corrosive for skin. Gas autoclave  Formaldehyde sterilization Uses 1) Fumigation of contaminated rooms & spaces. 2) Can be used in the same way as ethylene oxide (less frequently) in what is called low temperature steam and formaldehyde (LTSF). 3) Used to sterilize objects such as reusable medical devices, e.g. endoscopes.  Pharm PharmDDProgram Program (2024/2025) (2023/2024) Lecture’s References Pharmaceutical Microbiology. Edited by W.B.HUGO and A.D. Russell – Six Edition. 1998. 1 October 2024 www.su.edu.eg 43