Validation of sterilization - Pharmaceutical Microbiology Third Semester PDF Notes
Validation of sterilization
Contents
• Validation – meaning and significance
• Sterilization indicators
– Physical indicators
– Chemical indicators
– Biological indicators
Intended learning objectives
At the end of this lecture, the student will be able to:
• Explain the significance of validation in sterilization
• List the sterilization indicators
• Describe the working of sterilization indicators
Validation- History
• The concept of validation was first proposed by two Food and Drug Administration (FDA) officials, Ted Byers and Bud Loftus, in the mid-1970s in order to improve the quality of pharmaceuticals
• It was proposed in direct response to several problems in the sterility of large volume parenteral market
• The first validation activities were focused on the processes involved in making sterile products, but later on were applied for associated processes such as environmental control, media fill, equipment sanitization and purified water production
Validation of sterilization
• Validation means demonstrating that a process will consistently produce the results that it is intended to
• Validation is a process of establishing documentary evidence demonstrating that a procedure, process, or activity carried out in production or testing maintains the desired level of compliance at all stages.
• Validation would be necessary for each of the individual aspects of the manufacturing process,
• Environmental monitoring
• Raw materials quality assessment
• Sterilization process itself
• The sterility testing procedure
Sterilization indicators
Sterilization procedures should be monitored through a combination of physical, chemical, and biological techniques designed to evaluate the sterilizing conditions and the procedure's effectiveness
• Physical indicators
• Chemical indicators
• Biological indicators
Physical indicators
Observing the gauges or displays on the sterilizer for
• Assessing the cycle time
• Temperature
• Pressure of sterilization equipment
• Relative humidity
Heat sterilization
• A temperature record chart is made - part of the batch documentation
• Compared against a master temperature record (MTR)
• Information on heat distribution and penetration within a sterilizer can be gained by the use of thermocouples
Gaseous sterilization
• Measurement of elevated temperatures using temperature probes
• Routine leak tests to ensure gas-tight seals
• Pressure and humidity measurements are recorded.
• Gas concentration is measured, often by reference to weight of gas used
Radiation sterilization
• A plastic (often perspex) dosimeter is used
• It gradually darkens in proportion to the radiation absorbed
Integrity testing sterilizing filters
• Membrane filters have been used successfully for many years to remove yeast, bacteria and particulate from fluid streams
• To test the integrity of filters, the following tests are done:
a) Destructive test
b) Non - destructive integrity test
a) Destructive test- Destructive challenge testing is the best way to determine a sterilizing filter's ability to retain bacteria. During the bacterial retention test, 0.22 µm filter discs and devices are challenged with a solution of culture medium containing bacteria (Brevundimonas diminuta ATCC 19146) at a minimum challenge of 107 per cm2. The effluent is then passed through a second 0.45 µm filter disc that is placed on an agar plate and incubated.
- The filter cannot be used for filtration purposes again
b) Non - destructive integrity test, may be done on filters before and after filtration process
-This is done to ensure that the filter meets specification, is properly installed and intact during filtration, and to confirm the rating of the filter
- Integrity testing before filtration process monitors filter integrity, preventing use of a non-integral filter.
- Integrity testing after a batch has been filtered can detect if the integrity of the filter has been compromised during the process
There are 3 major tests used to determine the integrity of a membrane filter: the Bubble Point Test, the Forward Flow Test, and the Pressure Hold Test
• All three tests are based on the same physics, the flow of a gas through a liquid-wetted membrane under applied gas pressures
• They differ in which part of the flow/pressure spectrum they examine
• This is an indirect method for the measurement of pore size of filter
Bubble point pressure test
• Bubble point test is based on the fact that liquid is held in the pores of the filter by surface tension and capillary forces
• The minimum pressure ( as seen on the pressure dial) required to force liquid out of the pores is a measure of the pore diameter
The bubble point is expressed as :
Where
k = shape correction factor
Ύ = surface tension
cos ɵ = liquid solid contact angle
d = pore diameter
• Consists of immersing the filter candles in water or filling the funnel with the liquid in the case of a membrane filter or sintered glass filter
• Air or gas is passed from the bottom of the filter
• The pressure of Air/ gas is gradually increased until the first bubble is seen at the filter/liquid interface
Filtration sterilization
• Bubble point pressure test
Chemical indicators
• Chemical indicators are designed to respond to a characteristic change to one or more of the physical conditions within the sterilizing chamber
• The principle is based on the ability of heat, steam, gases and ionization radiation to alter the chemical and/or physical characteristics of chemical substances
• Change should take place only when satisfactory conditions for sterilization prevail
• Used for monitoring a sterilization process
• Chemical indicators generally undergo melting or colour changes
• Included in strategically placed containers or packages
• Monitors the conditions prevailing at the coolest or most inaccessible parts of a sterilizer
Bowie Dick test: Organic chemical in a printing ink base impregnated into a carrier material. A combination of moisture and heat produces a darkening of the ink
Brown’s tube: Sealed tubes partly filled with a solution which changes colour at elevated temperatures; rate of colour change is proportional to temperature
Thermalog S: Consists of a blue dye in a waxy pellet. At autoclaving temperatures, and in the continued presence of steam, the pellet melts and travels along a paper wick forming a blue band the length of which is dependent upon both exposure time and temperature
Thermalog G: Same as Thermalog S. Used for gaseous sterilization
Biological indicators
• Consist of standardized bacterial spore preparations
• Usually in the form either of suspensions in water or culture medium or of spores dried on paper, aluminium or plastic carriers.
• As with chemical indicators, they are usually placed in dummy packs located at strategic sites in the sterilizer
• After the sterilization process, the aqueous suspensions or spores on carriers are aseptically transferred to an appropriate nutrient medium, which is then incubated and periodically examined for signs of growth.
• The bacterial species to be used in a BI must be selected carefully, as it must be non-pathogenic and should possess above-average resistance to the particular sterilization process.
Filtration sterilization
• Measuring the ability of a filter to produce a sterile filtrate from a culture of a suitable organism
• Serratia marcescens has been used for filters of 0.45mm pore size,
• Brevundimonas diminuta (formerly Pseudomonas diminuta) having a minimum dimension of 0.3mm is applied to filters of 0.22mm pore size.
Summary
• Validation means demonstrating that a process will consistently produce the results that it is intended to
• Sterilization indicators - Physical indicators, Chemical indicators, Biological indicators
• Physical indicators validate the temperature, pressure, radiation dose or filter pore size
• Chemical indicator - Based on the ability of heat, steam, sterilant gases and ionizing radiation to alter the chemical and/or physical characteristics of a variety of chemical substances
• Biological indicators - Consist of standardized bacterial spore preparations
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