Aulton's Pharmaceutics PDF - Validation of Sterilization Process

Sterilization in practice CHAPTER 17 viable microorganisms by incubating all or part of...

Sterilization in practice CHAPTER 17 viable microorganisms by incubating all or part of Box 17.2 the product with a nutrient medium. Testing for sterility is a destructive process. For an item to be Worked example shown not to contain organisms, unfortunately it has Consider steam sterilization. For an initial bioburden of to be destroyed. Due to the destructive nature of 104 spores of Geobacillus stearothermophilus, an the test and the probabilities involved in sampling inactivation factor of 1010 will be required to only a portion of a batch, it is only possible to say achieve a sterility assurance level of 10−6. that no contaminating microorganisms have been G. stearothermophilus has a D value of 1.5 for steam sterilization. found in the sample examined in the conditions of Thus according to Eq. 17.1, a 15-minute sterilization the test (British Pharmacopoeia Commission, 2017b). process (i.e. holding time) at 121 °C will be required Thus the measurement of sterility relies on statistical to achieve an inactivation factor of 1010 (i.e. 1015/1.5). probability. In other words, it is impossible to The process will therefore reduce the level of prove sterility since sampling may fail to select microorganisms by 10 log cycles. nonsterile containers, and culture techniques have limited sensitivity. In addition, not all types of microorganisms that might be present can be detected by conventional methods as not all microorganisms assurance for a sterilizing process to render a popula- are affected by a sterilization process in the same tion of products sterile. For pharmaceutical prepara- way. It is possible that some may not be killed or tions a SAL of 10−6 or better is required. This equates removed. For example, a filter pore size of 0.22 µm to not more than one viable microorganism per million is usually used for filtration sterilization, which means items/units processed. Practically, the lethality of a that smaller microorganisms such as viruses are sterilization process and in particular the number of allowed to pass through. log cycles required need to be calculated. Detailed sampling and testing procedures are The inactivation factor, which measures the reduc- given in pharmacopoeias, and further details can be tion in the number of microorganisms (of a known found in Chapter 14. For terminally sterilized D value; see Chapters 15 and 16) brought about by products, biologically based and automatically a defined sterilization process, can be calculated as documented physical proofs that show correct treat- follows: ment during sterilization provide greater assurance than the sterility test. This method of assuring sterility IF = 10t D is termed parametric release and is defined as the (17.1) release of a sterile product based on process compli- where IF is the inactivation factor, t is the contact ance with physical specifications. Parametric release time (for heat or gaseous process) or radiation dose is acceptable for all fully validated terminal steriliza- (for ionizing radiation) and D is the D value appropri- tion processes recommended by the European ate to the process employed. An example calculation Pharmacopoeia. is shown in Box 17.2. Calculation of the IF is based on one obtaining inactivation kinetics that follows a first-order process. Validation of a sterilization In reality, this is not always the case. In the food process industry, the calculation of the most probable effective dose (MPED) is preferred as it is independent of The British Pharmacopoeia (British Pharmacopoeia Copyright © 2017. Elsevier. All rights reserved. the slope of the survivor curve for the process. Commission, 2017a) states: However, to establish an MPED that will achieve the required reduction in a number of microorganisms The sterility of a product cannot be requires complex calculations. guaranteed by testing; it has to be assured by the application of a suitably Test for sterility of the product validated production process. It is essential that the effect of the chosen Sterility testing assesses whether a sterilized phar- sterilization procedure on the product maceutical or medical product is free from (including its final container or package) 289 Aulton's Pharmaceutics E-Book : The Design and Manufacture of Medicines, edited by Kevin M. G. Taylor, and Michael E. Aulton, Elsevier, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/trinitycollege/detail.action?docID=5253018. Created from trinitycollege on 2021-12-07 18:12:41.  PART THREE Pharmaceutical microbiology and sterilization is investigated to ensure effectiveness Box 17.3 and the integrity of the product and that the procedure is validated before being Information required for the validation of a applied in practice. sterilization process Commissioning data Clearly this statement points out that testing for Evidence that the equipment has been installed in sterility is not enough and a suitable production accordance with specifications process should be appropriately validated. Any changes Equipment is safe to use in the sterilization procedure (i.e. change in steriliza- Equipment functions within predetermined limits tion process, product packaging or load) require Performance qualification data revalidation. For pharmaceutical preparations, good Evidence that equipment will produce a product manufacturing practices (GMP) have to be observed with an acceptable assurance of sterility for the entire manufacturing process, not just the Physical performance qualification – evidence that sterilization procedure. the specified sterilization conditions have been met The process of validation requires that the throughout the sterilization cycle: appropriate documentation is obtained to show that a the tests performed depend on the sterilization process is consistently complying with predetermined process specifications. International organizations such as the data should be generated from the worst region International Organization for Standardization (http:// in the sterilizer www.iso.org) and the Food and Drug Administration the data generated should also show no detrimental effect on the product and its in the USA (http://www.fda.gov) provide detailed packaging documentation for the validation of sterilization of Biological performance qualification – evidence that health care products or medical devices with various the specified sterilizing conditions deliver the processes (e.g. steam, radiation and gaseous steriliza- required microbiological lethality to the preparation/ tion). For the validation of sterilization processes, product: two types of data are required: commissioning data makes use of biological indicators and performance qualification data (Box 17.3). data are not required if the process is well Commissioning data refer mainly to the installa- defined (e.g. use of F value). tion and characteristics of the equipment, and the performance data ensure that the equipment will produce the required sterility assurance level. The performance qualification data can be divided into are carried out to demonstrate that all parts of the physical and biological performance data (Box 17.3). sterilizer have been correctly installed (installation Obtaining biological performance data is required qualification) and that they operate properly, with for the validation and revalidation of the sterilization sterilizing conditions reaching every part of the load process for new preparations, new loads and new (operation qualification; McDonnell, 2007). The test sterilization regimens and is usually not used routinely methods used vary according to the sterilization except when the sterilization conditions are not well method and may involve the use of physical indicators, defined (e.g. gaseous sterilization) or with nonstandard chemical indicators and biological indicators. methods. The use of biological indicators (discussed Physical indicators measure parameters such as in the next section) requires good knowledge of the heat distribution (i.e. temperature) by thermocouples, inactivation kinetics (e.g. D value) for a given process. pressure variation by gauges or transducers, gas Copyright © 2017. Elsevier. All rights reserved. Performance qualification data must be reevaluated concentration, steam purity, relative humidity by following a change to the preparation or product and hygrometers or direct calorimetry, delivered dose and its packaging, the loading pattern or the sterilization time exposure. Sensors must be maintained and cycle. calibrated regularly. They are usually the first indicators of a problem with a sterilization process. Sensors maintenance and calibration are essential to ensure Process indicators the validity of parametric release (Berube et al., 2001). Chemical indicators vary depending on the steriliza- For all methods of sterilization, it is essential that tion method but essentially they all change in physical the equipment used works correctly. Routine tests or chemical nature in response to one or more 290 Aulton's Pharmaceutics E-Book : The Design and Manufacture of Medicines, edited by Kevin M. G. Taylor, and Michael E. Aulton, Elsevier, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/trinitycollege/detail.action?docID=5253018. Created from trinitycollege on 2021-12-07 18:12:41.  Sterilization in practice CHAPTER 17 a b c Fig. 17.5 Examples of chemical and biological indicators. (a) Multiparameter (time, steam and temperature) indicators. (b) Sterilization control tubes. (c) Geobacillus stearothermophilus/Bacillus stearothermophilus biological indicators. parameters. There are several types of chemical indicators (Fig. 17.5); temperature-specific indicators just show whether a specific temperature has been reached (single-variable indicators), whereas multiparameter/multivariable indicators can measure Unexposed Fail Pass more than one variable at a time, e.g. heat and time Fig. 17.6 Bowie–Dick test pack used to monitor air or gas concentration and time, or time, steam and removal from steam sterilizers; a uniform colour change temperature. indicates sufficient steam penetration. Process indicators demonstrate that an indica- tor has gone through a process but they do not guarantee that sterilization was satisfactory. A Other chemical indicators are quantitative and indicate common example is autoclave tape (single end-point a combination of critical variables within a process. indicator), which reflects the conditions inside the This is the case with dosimeters (e.g. Perspex®), which chamber environment but is not able to demonstrate gradually change colour on exposure to radiation. that an item has been sterilized. Another example The performance of chemical indicators can be altered is a Temptube®, which is a glass tube containing a by the storage conditions before and after use and chemical with a specific melting point indicated by the method used. by a colour change. More specific indicators, such Biological indicators consist of a carrier or package as the ‘Bowie–Dick tests’, are used to monitor air containing a standardized preparation of defined removal from autoclaves. They must be used in the microorganisms of known resistance to a specific mode Copyright © 2017. Elsevier. All rights reserved. first cycle of the day as an equipment function test of sterilization (Berube et al., 2001; see Fig. 17.5). (McDonnell, 2007). The standardized test pack is The carriers used are usually made of filter paper, a placed in the centre of porous load sterilizers, and if glass slide, stainless steel or a plastic tube. Some the process is correct (i.e. air removal is appropriate), new versions incorporate ampoules containing a uniform colour change occurs across the test package growth medium. The carrier is covered to prevent (Fig. 17.6). deterioration or contamination while still allowing A common example of multivariable indicators is entry of the sterilizing agent (British Pharmacopoeia sterilization control tubes (e.g. Browne’s tubes), which Commission, 2017a). Different organisms are used produce a colour change when the appropriate for different processes (Table 17.6), but biological temperature and exposure time have been achieved. indicators usually consist of bacterial spores. In excess 291 Aulton's Pharmaceutics E-Book : The Design and Manufacture of Medicines, edited by Kevin M. G. Taylor, and Michael E. Aulton, Elsevier, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/trinitycollege/detail.action?docID=5253018. Created from trinitycollege on 2021-12-07 18:12:41.  PART THREE Pharmaceutical microbiology and sterilization Table 17.6 Organisms used as biological indicators for as Brevundimonas diminuta, is a small (0.2 µm to sterilization 0.9 µm) Gram-negative short rod that is a natural choice for this test because of its size and because Sterilization Spores used as a biological indicator it was originally isolated from contaminated filtered process solutions (Levy, 2001). After filtration of a bacterial Dry heat Bacillus atrophaeus ATCC 9372. suspension prepared in tryptone soya broth, the filtrate NCIMB 8058 or CIP 77.18 is collected and incubated at 32 °C. Moist heat Geobacillus stearothermophilus ATCC Integrity tests are used to verify the integrity of 7953. an assembled sterilizing filter before use and to NCTC 10007. NCIMB 8157 or CIP 52.81 confirm integrity after use. The tests used must be Ethylene oxide Bacillus atrophaeus ATCC 9372. appropriate to the filter type and the stage of testing NCIMB 8058 or CIP 77.18 and may include bubble point tests, pressure hold tests and diffusion rate tests. The bubble point test Radiation Bacillus pumilus ATCC 27142. NCTC is the oldest and one of the most widely used non- 10327. destructive tests. It measures the pressure (bubble- NCIMB 10692 or CIP 77.25 point pressure) needed to pass gas through the largest Filtration Pseudomonas diminuta ATCC 19146. pore of a wetted filter. In practice, the pressure NCIMB 11091 or CIP 103020 required to produce a steady stream of gas bubbles through a wetted filter is often used as the bubble point. The basis of the test relies on the holes through the filter resembling uniform capillaries passing from of between 105 and 107 spores are used, the recom- one side to another. If these capillaries become wet, mended number being dependent on the sterilization then they will retain liquid via surface tension, and method being assessed. After exposure to the steriliza- the force needed to expel the liquid with a gas is tion process, the indicators are removed aseptically proportional to the diameter of the capillaries (pore and incubated in suitable media to detect the presence diameter). The main limitations of this technique of surviving microorganisms. If no growth occurs, are that it is reliant on operator judgement and on the sterilization process is said to have had sufficient the holes in the filter being perfect uniform capillaries lethality (Berube et al., 2001). (Walsh & Denyer, 2013). Diffusion rate tests are especially useful for large- Testing filtration efficacy area filters. They measure the rate of flow of a gas as it diffuses through the water in a wetted filter. Compared with other sterilization methods, the poten- The pressure required to cause migration of the gas tial risk of failure is higher for filtration sterilization. through the liquid in the pores can be compared with This means that it may be advisable to add an extra data specified by the filter’s manufacturer to establish prefiltration stage using a bacteria-retentive filter. if the filter has defects (Levy, 2001). Confidence in the filters used is of prime importance during filtration sterilization. Each batch of filters is tested to ensure that they meet the specifications for Monitoring decontamination release of particulate materials, mechanical strength, chemical characteristics (e.g. oxidizable materials and The possibility of transmission of Creutzfeldt–Jakob leaching of materials) and filtration performance. The disease (CJD) has increased the importance of protein Copyright © 2017. Elsevier. All rights reserved. methods for testing filtration performance involve removal from previously contaminated high-risk either a challenge test (which is destructive so cannot instruments. Visual inspection and ninhydrin or be conducted on every filter in a batch) or an integrity modified o-phthalaldehyde (OPA) methods may not test (Walsh & Denyer, 2013). be as sensitive as newer methods. Scanning electron The microbial challenge test is used to demonstrate microscopy (SEM) and energy-dispersive X-ray that a filter is capable of retaining microorganisms. spectroscopy (EDX) analysis are not practical for This is normally performed with a suspension of at health care professional use, so recent methods have least 107 colony-forming units (see Chapter 14) of concentrated on using fluorescent reagents coupled Pseudomonas diminuta per square centimetre of active with digital imaging; for example, epifluorescence filter surface. Pseudomonas diminuta, also known differential interference contrast microscopy (EFDIC) 292 Aulton's Pharmaceutics E-Book : The Design and Manufacture of Medicines, edited by Kevin M. G. Taylor, and Michael E. Aulton, Elsevier, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/trinitycollege/detail.action?docID=5253018. Created from trinitycollege on 2021-12-07 18:12:41.  Sterilization in practice CHAPTER 17 Table 17.7 Limitations of sterilization processes Sterilization processes Limitations Heat sterilization Steam Heat; damage to preparation Vapour; damage to the container (wetting of final product, risk of contamination after sterilization) Pressure; air ballasting: damage to the container Dry heat Heat: damage to preparation Potentially longer exposure time needed Gaseous sterilization Ethylene oxide High toxicity: risk to the operator Decontamination required after the process Explosive: risk to the operator Slow processa Many factors to control Formaldehyde High toxicity: risk to the operator Damage to some materials (e.g. materials made from cellulose) Decontamination required after the process Slow processa Many factors to control Radiation sterilization γ-radiation Risk to the operator Water radiolysis: damage to the product Discolouration of some glasses and plastics (including PVC), destructive process may continue after sterilization has finished Liberation of gases (e.g. hydrogen chloride from PVC) Hardness and brittleness properties of metals may change Butyl and chlorinated rubber are degraded Changes in potency can occur High costs Particle radiation β-radiation: risk to the operator Water radiolysis: damage to the product Poor penetration of electrons exacerbated by density of product Significant product heating may occur at high doses High costs Chemosterilants Glutaraldehyde and Toxicity: risk to the operator o-phthaladehyde Activity: reports of microbial resistance Peracetic acid Corrosiveness: damage to the product/device Activity: reports of microbial resistance Copyright © 2017. Elsevier. All rights reserved. Filtration sterilization Not efficient for small particles (viruses, prions) Requires strict aseptic techniques Integrity of membrane filter Growth of microbial contaminants in depth filter Shedding of materials from depth filter a Relative to moist heat sterilization. 293 Aulton's Pharmaceutics E-Book : The Design and Manufacture of Medicines, edited by Kevin M. G. Taylor, and Michael E. Aulton, Elsevier, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/trinitycollege/detail.action?docID=5253018. Created from trinitycollege on 2021-12-07 18:12:41.