L6 - Sterilization and Disinfection Lecture Notes PDF

L6- Sterilization and disinfection Dr. Janita Pinto September 11, 2024 www.gmu.ac.ae COLLEGE OF PHARMACY Learning objectives At the end of the session the student will be able to Comp...

L6- Sterilization and disinfection Dr. Janita Pinto September 11, 2024 www.gmu.ac.ae COLLEGE OF PHARMACY Learning objectives At the end of the session the student will be able to Compare and contrast the differences between cleaning, disinfection and sterilization Understand the sterilization processes used in the pharmaceutical industry Discuss the required monitoring processes utilized in disinfection and sterilization What is Sterilization, Disinfection & Antisepsis? Sterilization : Process by which an article, surface or medium is freed of all organisms including spores Disinfection : Destruction of all pathogenic organisms or organisms capable of giving rise to infection. Antisepsis : Prevention of infection usually by inhibiting growth of bacteria. Bactericidal agents : Kills bacteria Bacteriostatic agents : Prevents multiplication of bacteria Microbial control methods  Choice of method for manufacturing a sterile product Two strategies are available for manufacturing sterile products: Terminal sterilization, in which the product is made, packed in its final container, then sterilized; or Aseptic manufacture where the product is made from individual sterile ingredients using aseptic techniques  Terminal sterilization Heat (either as steam or hot air), radiation and microbicidal gases may be used Desirable properties of a sterilization method: reliable in terms of achieving the required sterility assurance level of 10-6 ; safe for the operators; safe in terms of inducing no damage to the product or its container, or inducing the formation of toxic residues; an easily understood process that can readily be controlled and monitored by physical instruments; short exposure time; low cost. Terminal sterilization Bacterial spores are the most heat resistant of all organisms, so heat sterilization processes are designed with the aim of killing spores. Medical devices containing plastics, cannot be heated, so radiation and ethylene oxide gas are used as alternatives. Prions are more resistant than bacterial spores and have such an exceptionally high heat and radiation tolerance that sterilization processes designed to inactivate them would be likely to do severe damage to the product being sterilized. Sterile filtration - heat-sensitive water-soluble drugs Ophthalmic creams etc aseptic manufacture may be the best option, although radiation is becoming more frequently used as a result of regulatory pressure to adopt terminal sterilization processes. Terminal sterilization methods Steam sterilization Dry heat sterilization Radiation sterilization Gaseous sterilization Filtration sterilization and aseptic manufacture  Steam sterilization Autoclave: Steam under pressure Pressure:15 pounds per square inch Temperature & time: 121ο C for 20 min Principle The principle of the autoclave or steam sterilizers is that water boils when its vapour pressure equals that of the surrounding atmosphere. When pressure is inside the closed vessel increases, the temperature at which water boils also increases. Steam is very much better as a sterilizing agent than water at the same temperature, because steam has a high latent heat content which is transferred to the objects being sterilized when the steam condenses on them. It is essential that air is removed from the autoclave chamber and completely replaced by steam during the operating cycle Steam sterilization Method Typical conditions Common applications Aqueous solutions in sealed containers (bottled fluids) Dry, saturated Steam (heating in Surgical and dental instruments steam at 121 C an autoclave) Dressings (porous loads) for 15 minutes Decontamination of infected materials or laboratory waste The validation of an autoclave Physical monitoring of the machine’s performance Load configuration Biological indicators Dry heat sterilization This method simply involves heating the item to be sterilized in a hot air oven Holding Time – 120 Min at 160ο C ,1 hour at 170 ο C or 30 minutes at 180 ο C The temperatures and times required are longer because : (i) dry heat kills microorganisms by oxidative processes which are less efficient than the hydrolytic mechanisms of steam and (ii) dry air does not possess latent heat. Dry heat sterilization Method Typical conditions Common applications 160° C for two hours, or, in Glassware Dry heat (hot air a combined sterilization Oils, fats and waxes, oven) and glass depyrogenation and oily injections cycle, 250°C for 30 minutes Items to be sterilized by dry heat need to be appropriately wrapped or sealed in containers that prevent recontamination after processing. Radiation sterilization Gamma-rays or high-energy electrons are used to sterilize Gamma radiation is rarely used for heat-sensitive materials and water-containing products products like medical devices (for because the products of radiolysis eg, syringes), surgical instruments, of water usually cause too much anhydrous medicines (such as damage to the drug. ointments) and powders. Radiation sterilization Ionization of atoms or molecules by gamma rays and high-energy electrons occurs without inducing radiation in the exposed material. The mechanism by which radiation kills cells is that of ionization causing free radical production and damage to the DNA, although both human and microbial cells have damage-repair mechanisms The relative merits of gamma and electron beam irradiation Gamma Electron beam Source Cannot be switched off, so it needs to be contained in a Can be switched off, so it poses no building having reinforced concrete walls and submerged radiation risk when not in use in a storage pool of water when not in use Speed Relatively slow: may require several hours’ exposure A sterilizing dose may be given in minutes or even seconds Penetration Good Relatively poor so it is unsuitable for sterilizing dense materials, particularly medical devices containing metals Product damage Relatively long exposures can cause unacceptable Usually, less damage than with gamma product damage Environment and Spent fuel rods have to be disposed of. Public concern These problems do not arise public acceptability about radioactive materials. Gaseous sterilization Several microbicidal gases have been used for sterilization including Ethylene oxide- the most common Formaldehyde-Formaldehyde gas for use in sterilization is produced by heating formalin to a temperature of 70 – 75 ° C with steam, leading to the process known as LTSF. Hydrogen peroxide– 35%w/v, and peracetic acid 3.5%w/v, are used as highly effective oxidizing agents to kill microorganisms  Gaseous sterilization Ethylene oxide is suitable for sterilizing materials that are both heat and radiation sensitive It is also infrequently used in hospitals for surgical instruments and the sterilization of isolators and chambers, although hydrogen peroxide is now preferred. Ethylene oxide is a colourless gas that is explosive when mixed with air in proportions greater than 3.6% by volume, so it is normally used as a mixture with carbon dioxide, nitrogen or dichlorodifluoromethane to minimize the risk. The gas is both mutagenic and carcinogenic.  Ultraviolet light UV light is a nonionizing form of electromagnetic radiation that has even poorer penetrating power than accelerated electrons. Specific molecular damage occurs on the pyrimidine bases (thymine and cytosine), which form abnormal linkages with each other called pyrimidine dimers It is commonly used for the disinfection of surfaces in aseptic work areas, air and for decontamination of water to be used both as an ingredient of medicines and for cleaning purposes. UV treatment cannot be used to produce endotoxin-free water for injection.  Filtration sterilization and aseptic manufacture For drugs containing proteins (for eg: interferons) and other biological polymers (for eg: DNA-vaccines), the only sterilization option is to use filtration and then manufacture the product aseptically using sterile ingredients. Filtration is a common means of sterilizing injections and eye drops as well as air and other gases.  Filtration sterilization and aseptic manufacture Modern sterilization-grade filters are cellulose derivatives and polymers like Polytetrafluoroethylene, polycarbonate and polyethersulfone. The advantage of using synthetic polymers is that the pore diameter and density (pores per square millimetre) can be quite precisely controlled  Depth filters and membrane filters. Depth filters made from ceramics, glass or metal and have a significant thickness relative to their pore size, whereas a membrane filter, normally of a synthetic polymer, is comparatively thin. Both have characteristics of an ideal filter: good particle removal (sterilizing efficiency) mechanical strength easily sterilized in situ by steam, Some characteristics of membrane and depth filters Characteristic Membrane Depth Absolute retention of microorganisms greater than rated pore size + – Rapid rate of filtration + – High dirt – handling capacity – + Grow- through of microorganisms Unlikely + Shedding of filter components – + Fluid retention – + Solute adsorption – + Good chemical stability Variable + (depends on membrane) Good sterilization characteristics+ + + + , applicable; –, not applicable. Filters Virus-retentive filters are available, which have nominal pore sizes of 0.01–0.02 mm An advantage afforded by filtration is that the method physically removes both living and dead cells from solution Thus a filter-sterilized solution would be expected to have a greater probability of passing a pyrogen or endotoxin test anyway, but this can be further enhanced by the use of positively charged polyvinylidene fluoride or nylon filters, which attract the negatively charged endotoxins Filters Filtration is used to supply sterile air to pharmaceutical manufacturing suites (‘clean rooms’) and isolators, operating theatres and microbiological safety cabinets. Depth filters, typically made of glass microfibres separated by aluminium sheets, are normally used for gas filtration. High efficiency particulate air (HEPA) filters typically remove 99.97% of airborne particles of 0.3 mm in diameter. Filters Filtration is not a terminal sterilization process. Solutions that are filter sterilized still have to be dispensed into their containers and, there is the opportunity for contamination to arise during this process. Sterile products’ manufacturers are required to undertake process simulations ( ‘media fills’) in which the same factory filling line that would be used to fill the product in question is first tested by dispensing sterile culture medium into, typically, 5000– 10,000 sterile containers. Because filtration is inherently less reliable than terminal sterilization processes, products sterilized in this way must be subjected to a test for sterility  Biological indicators of sterilization The names of these organisms have been changed, so the former names will still be found in older textbooks: Geobacillus stearothermophilus = B. stearothermophilus; Bacillus atrophaeus = B. subtilis var niger DISINFECTANTS and ANTISEPTICS A. Alcohols, Aldehydes, and Acids Ethanol (70%) and isopropanol (70-90%) are effective skin antiseptics because they denature microbial proteins. Formaldehyde, which also denatures proteins, is too irritating for topical use but is a disinfectant for instruments. Acetic acid (1%) is used in surgical dressings and has activity against gram-negative bacteria, including Pseudomonas. DISINFECTANTS and ANTISEPTICS B. Halogens Iodine tincture is an effective antiseptic for intact skin. Iodine complexed with povidone (povidone-iodine) is widely used, particularly as a preoperative skin antiseptic. Hypochlorous acid, formed when chlorine dissolves in water, is antimicrobial. This is the basis for the use of chlorine and halazone in water purification. Sodium hypochlorite is the active component in household bleach, a 1:10 dilution of which is recommended by the Centers for Disease Control and Prevention (CDC) for the disinfection of blood spills that may contain HIV or hepatitis B virus (HBV).  DISINFECTANTS and ANTISEPTICS C. Oxidizing Agents Hydrogen peroxide exerts a short-lived antimicrobial action through the release of molecular oxygen. The agent is used as a mouthwash, for cleansing wounds, and for disinfection of contact lenses. D. Heavy Metals Organic mercurials such as nitromersol and thimerosal frequently cause hypersensitivity reactions but continue to be used as preservatives for vaccines, antitoxins, and immune sera. In the past silver nitrate was commonly used for prevention of neonatal gonococcal ophthalmia, but it has been largely replaced by topical antibiotics. Silver sulfadiazine (a sulfonamide) is used to decrease bacterial colonization in burns. DISINFECTANTS and ANTISEPTICS E. Chlorinated Phenols Owing to its toxicity, phenol itself is used only as a disinfectant of inanimate objects. Hexachlorophene has been widely used in surgical scrub routines and in deodorant soaps, where it forms antibacterial deposits on the skin, decreasing the population of resident bacteria. Antiseptic soaps may also contain other chlorinated phenols such as triclocarban and chlorhexidine. DISINFECTANTS and ANTISEPTICS F. Cationic Surfactants Benzalkonium chloride and cetylpyridinium chloride are used as disinfectants of surgical instruments and surfaces such as floors and bench tops. G. Ultraviolet Irradiation Ultraviolet irradiation is used in some health care facilities as an alternate mode of disinfection for patient care areas.  Learning Resources Katzung BG, Kruidering-Hall M, Tuan R, Vanderah TW, Trevor AJ. eds. Katzung & Trevor's Pharmacology: Examination & Board Review, 13e. McGraw Hill; 2021.. https://accesspharmacy-mhmedical- com.gmulibrary.com/content.aspx?bookid=3058&sectionid=255303791 Bennett JE, Dolin R, Blaser MJ. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Updated 8th Edition. Elsevier Saunders; 2015. ISBN 978-0-323-40161-6. https://www.clinicalkey.com/#!/content/book/3-s2.0-B9780323401616003260 Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 8th ed. Elsevier Ltd; 2016. ISBN: 978-0-323-29956-5. https://www.clinicalkey.com/#!/content/book/3-s2.0- B9780323299565000033 Additional Reading Baveja CP. Textbook of Microbiology for Dental Students; 2019 edition. New Delhi, India: Arya Publications. ISBN-13: 978-8178556734 9/11/2024