STERILIZATION

STERILIZATION: 

STERILIZATION PRESENTED BY: SHILPI BHATNAGAR M.PHARM (Q.A.) 1 ST SEM

INTRODUCTION: 

INTRODUCTION STERILISATION is a process by which living organisms are killed or removed to the extend that they are no longer detected by standard culture media which have previously been found to proliferate. Reliable sterilization depends on contact of the sterilizing agent with all surfaces of the item to be sterilized. Selection of the agent to achieve sterility depends primarily upon the nature of the item to be sterilized.

METHODS OF STERILIZATION: 

METHODS OF STERILIZATION Commonly used method of sterilization are: Dry heat sterilization Moist heat sterilization Ethylene oxide sterilization Irradiation sterilization Filtration sterilization

Dry heat sterilization : 

Dry heat sterilization Dry heat in the form of hot air is used primarily to sterilize anhydrous oils, petroleum products, and bulk powders that steam and ethylene oxide gas cannot penetrate. Death of microbial life by dry heat is a physical oxidation or slow burning process of coagulating the protein in cells. In the absence of moisture, higher temperatures are required than when moisture is present because microorganisms are destroyed through a very slow process of heat absorption by conduction.

Moist heat sterilization : 

Moist heat sterilization Heat destroys microorganisms, but this process is hastened by the addition of moisture. Steam in itself is inadequate for sterilization. Death by moist heat in the form of steam under pressure is caused by the denaturation and coagulation of protein or the enzyme-protein system within the cells. These reactions are catalyzed by the presence of water. Steam is water vapour; it is saturated when it contains a maximum amount of water vapour. Direct saturated steam contact is the basis of the steam process. Steam, for a specified time at required temperature, must penetrate every fibres and reach every surface of items to be sterilized. When steam enters the sterilizer chamber under pressure, it condenses upon contact with cold items. This condensation liberates heat, simultaneously heating and wetting all items in the load, thereby providing the two requisites: moisture and heat.

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No living thing can survive direct exposure to saturated steam at 250 F (121 º C) longer than 15 minutes. As temperature is increased, time may be decreased. A minimum temperature-time relationship must be maintained throughout all portions of load to accomplish effective sterilization. Exposure time depends upon size and contents of load, and temperature within the sterilizer. At the end of the cycle, re-evaporation of water condensate must effectively dry contents of the load to maintain sterility.

Ethylene oxide sterilization: 

Ethylene oxide sterilization Ethylene oxide is used to sterilize items that are heat or moisture sensitive. Ethylene oxide (EO) is a chemical agent that kills microorganisms, including spores, by interfering with the normal metabolism of protein and reproductive processes (alkylation) resulting in death of cells. Used in the gaseous state, EO gas must have direct contact with microorganisms on or in items to be sterilized. Because EO is highly flammable and explosive in air, it must be used in an explosion-proof sterilizing chamber in a controlled environment. When handled properly, EO is a reliable and safe agent for sterilization, but toxic emissions and residues of EO present hazards to personnel and patients. Also, it takes longer than steam sterilization, typically, 16-18 hrs. for a complete cycle.

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EO gas sterilization is dependent upon four parameters: EO gas concentration, temperature, humidity, and exposure time. Each parameter may be varied. Ethylene oxide can be used with a wide range of plastics (e.g. petri dishes, pipettes, syringes, medical devices, etc.) and other materials without affecting their integrity.

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Low Temperature Gas Plasma (LTGP) is used as an alternative to ethylene oxide. It uses a small amount of liquid hydrogen peroxide (H 2 O 2 ), which is energized with radio frequency waves into gas plasma. This leads to the generation of free radicals and other chemical species, which destroy organisms.

Irradiation sterilization : 

Irradiation sterilization Irradiation : It usually destroys or distorts nucleic acids. Ultraviolet light is commonly used to sterilize the surfaces of objects,  although x-rays, gamma radiation and electron beam radiation are also used. Ultraviolet lamps are used to sterilize workspaces and tools used in microbiology laboratories and health care facilities. UV light at germicidal wavelengths (two peaks, 185 nm and 265 nm) causes adjacent thymine molecules on DNA to dimerize , thereby inhibiting DNA replication (even though the organism may not be killed outright, it will not be able to reproduce). However, since microorganisms can be shielded from ultraviolet light in fissures, cracks and shaded areas, UV lamps should only be used as a supplement to other sterilization techniques.

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Gamma radiation and electron beam radiation are forms of ionizing radiation used primarily in the health care industry. Gamma rays, emitted from cobalt-60, are similar in many ways to microwaves and x-rays. Gamma rays delivered during sterilization break chemical bonds by interacting with the electrons of atomic constituents. Gamma rays are highly effective in killing microorganisms and do not leave residues or have sufficient energy to impart radioactivity.

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Electron beam (e-beam) radiation , a form of ionizing energy, is generally characterized by low penetration and high-dose rates. E-beam irradiation is similar to gamma radiation in that it alters various chemical and molecular bonds on contact. Beams produced for e-beam sterilization are concentrated, highly-charged streams of electrons generated by the acceleration and conversion of electricity. e-beam and gamma radiation are for sterilization of items ranging from syringes to cardiothoracic devices.

Filtration sterilization : 

Filtration sterilization Filtration involves the physical removal (exclusion) of all cells in a liquid or gas. It is especially important for sterilization of solutions which would be denatured by heat (e.g. antibiotics, injectable drugs, amino acids, vitamins, etc.). Portable units can be used in the field for water purification and industrial units can be used to "pasteurize" beverages. Essentially, solutions or gases are passed through a filter of sufficient pore diameter (generally 0.22 micron) to remove the smallest known bacterial cells.

General consideration about sterilization:: 

General consideration about sterilization: All sterilization processes should be validated. It becomes all the more necessary when the method of sterilization is not in accordance with pharmacopoeial or national standards and the preparation is not a simple aqueous or oily solution. Suitability of sterilization method and its efficacy should be demonstrated before it is employed. This may be repeated at regular intervals, at least once a year. This should also be done when significant modifications have been made in the equipment. Records of the results should be kept. Biological indicators, if used should be considered only as additional method of monitoring sterilization and should be replace physical controls. When these are used, precautions should be taken so that microbial contamination is not transferred from them.

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There should be method by which the products which have been sterilized and which have not been are identified clearly. Each basket, tray or other container containing the product should be labelled with the name of the product, its batch number and status whether sterilized or not.

REFERENCES: 

REFERENCES P.P Sharma, How to practice GMPs, 5 th edition, vandana publications pvt . ltd., delhi , page no. 277-281 www.textbookofbacteriology.net www.authorstream.com http://www.urmc.rochester.edu/sterile and material processing department

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