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Process Validation: Terminal Sterilization Processes for Pharmaceutical Products
GUIDE-0074
Contact Information and Complete Document for Printing
Table of Contents
1. Introduction
2. Glossary of Terms
3. Validation Approaches
4. Protocol Development and Control
5. Personnel and Personnel Documentation
6. Data Review and Study Certification
7. Laboratory
8. Equipment Qualification
9. Equipment Calibration
10. Facilities
11. General Considerations Prior to Process Validation
12. Biological Challenge Reduction Studies
13. Process Validation: Sterilization by Moist Heat
14. Process Validation: Sterilization by Irradiation
15. Process Validation: Sterilization by Ethylene Oxide and Other Gases
16. Post Validation Process Monitoring
17. Requalification and Revalidation
1. Introduction
The purpose of this document is to provide guidance to manufacturers of pharmaceutical dosage forms regarding how to establish the scientific effectiveness, as required by the Health Products and Food Branch Inspectorate (Inspectorate), of terminal sterilization processes when used to produce pharmaceutical products or sterilize primary packaging materials. It includes the type of information which needs to be gathered and the supporting documentation which must be submitted to the Branch for approval of the process and for inclusion in the Good Manufacturing Practices (GMP) for the manufacture of that pharmaceutical.
The reader should understand that it is impossible to state in one document all of the specific elements required in the validation of terminal sterilization processes. The goal of validation is to demonstrate that a process, when operated within established limits, produces a product of consistent and specified quality. During validation, the critical process parameters must be identified, and, based on sound scientific principles, appropriate studies must be performed to demonstrate that the parameters can be met on a consistent basis.
Process validation must be considered as early in the development of a new product or a new or modified process as is practical. In this way, data required for validation can be collected during development studies, and also during the production of clinical and commercial batches. This "prospective" validation approach is preferred by the Inspectorate and other Directorates since it demonstrates a well thought-out product production process.
In preparing this document, we have assumed that the reader is familiar with the applications, limitations, and effects of all methods of terminal sterilization including moist heat, radiation, and gaseous sterilization.
The objective of any processes pertaining to terminal sterilization is to control the pre-sterilization bioburden to an appropriate level. It is important that the level of microbial quality be critically evaluated first, in order that the use of the terminal sterilization process may be rationally applied. Knowledge of the microbial quality of the materials and components has significant importance. A reduction of the microbial bioburden of these materials and components will allow for a more effective terminal sterilization. The probability of survival is a function of the number and types (species) of microorganisms present on the product. It is important to track the species as well as the number of organisms in order to assure that the terminal sterilization parameters continue to provide the same Sterility Assurance Level (SAL).
This document replaces the previous version of Process Validation: Gaseous Sterilization for Pharmaceuticals (GUI- 0007), Process Validation: Irradiation Sterilization for Pharmaceuticals (GUI- 0009) and Process Validation: Moist Heat Sterilization for Pharmaceuticals (GUI- 0010).
2. Glossary of Terms
Batch: Defined quantity of bulk intermediate, or finished product, that is intended or purported to be uniform in character and quality, and which has been produced during a defined cycle of manufacture.
Bioburden: The total number of viable microorganisms on or in a pharmaceutical product or in the manufacturing environment prior to sterilization processing.
Biological Indicator: A device consisting of a number of microorganisms (bacterial spores) of known resistance to the sterilization method to monitor adequacy of sterilization.
Dvalue: The decimal reduction time or time required to reduce a microbial population by 90% (one log value) under specified test conditions.
DmaxT: The maximum dose tolerated by the product before product degradents increase to significant levels. (Sterilization by Irradiation)
DmaxP: The maximum process dose allowed. This dose is a judgment call. It is set below the DmaxT, to prevent damage to the product, but is large enough to ensure that the DminP will achieve the desired SAL. (Sterilization by Irradiation)
DminP: The minimum process dose. This dose is determined by the configuration of the irradiation facility and the loading pattern/density of the product. (Sterilization by Irradiation)
F0 The amount of time in minutes, equivalent to time at 121oC, to which a unit has been exposed during a sterilization cycle. (Sterilization by Moist Heat)
kGy: The Gray (Gy) is the international unit for measuring the radiation dose delivered. 1 kGy=100,000 rads or 0.1 MRad (old terminology).
Sterility Assura Level (SAL): Expected probability of a surviving microorganism on each individual product after exposure to a valid sterilization process.
3. Validation Approaches
3.1 The validation of a product-specific sterilizing processes may be performed using either the Prospective or Concurrent Validation approach. Sterilization is an example of a process for which efficacy cannot be verified by retrospective evaluation of documentation and testing of the product. It is important to be aware that exposure to a validated and accurately controlled sterilization process is not the only factor associated with the provision of assurance that the product is sterile and suitable for its intended use. The most appropriate approach should be selected, and this selection must be justified and documented. Please refer to the Validation Guidelines for Pharmaceutical Dosage Forms (GUI-0029) for this selection. The validation is conducted, documented and evaluated, and the validation process and end-product is approved by the validation team.
3.1.1 Prospective Validation of the sterilization process applies when new products or new formulations of existing products are being developed or when a change is made to an existing sterilization process that may affect the quality or the sterility of a drug.
3.1.2 Concurrent Validation of the sterilization process applies to existing products when an intended change other than to the sterilization process is expected to have no effect on the quality or the sterility of a drug.
4. Protocol Development and Control
4.1 Validation of a product specific sterilization process must be based on detailed protocol that is approved prior to execution.
4.2 Changes to the validation protocol require a written change control procedure. The purpose of the change control procedure should be to reduce the risk of unauthorized deliberate, or inadvertent change(s) being made to the protocol, methods and/or procedures, the sterilization process, and the product/materials/supplies.
4.3 The Process Validation Protocol should contain:
4.3.1 a detailed description of the sterilization process and environment;
4.3.2 the process objectives in terms of product type, batch size, container/closure system, and the required Sterility Assurance Level (SAL);
4.3.3 pre-established specifications and parameters for the sterilization process such as: temperature limits, minimum/maximum exposure, maximum acceptable pre-sterilization product bioburden, etc;
4.3.4 a description of the equipment and relevant support systems which will be used for the sterilization process. This description should include relevant performance characteristics of each system, sub-system or piece of equipment such as gauge sensitivity and response, valve operation, alarm system functions, timer response and accuracy, cycle controller functions, air break systems and filters;
4.3.5 requirements for equipment calibration;
4.3.6 a description of the methodology for monitoring the performance of the equipment and the entire sterilization process with a defined sequence and timing of activities;
4.3.7 a list and description of all validated test methods, in-process controls, sampling procedures, and tabulation of data collected;
4.3.8 a listing of the validation team members and personnel responsible for coordinating, performing, evaluating and certifying each activity identified in the protocol;
4.3.9 any additional information that may be relevant to the sterilization process.
5. Personnel and Personnel Documentation
5.1 Qualified personnel are responsible for all validation activities. Records supporting these qualifications should be maintained.
5.2 Personnel with appropriate training and experience should ensure that all validation activities are based on sound engineering and scientific principles;
5.3 All personnel conducting validation activities should be trained and experienced in their specific duties and responsibilities.
5.4 The effectiveness of the training program should be monitored, reviewed, and documented with adequate corrective actions implemented.
6. Data Review and Study Certification
6.1 All information and data generated as part of the validation program must be evaluated by qualified individuals against protocol requirements, and judged as meeting or failing these requirements. Written evidence supporting the evaluations and judgments must be available.
6.1.1 The evaluations should be performed as the information becomes available.
6.1.2 If evaluations show that protocol requirements were not met, the impact on the sterilization process should be investigated and documented. The change control procedure must be followed when protocol modifications are necessary.
6.1.3 Failure to adhere to the procedure or criteria as laid down in the validation protocol must be considered as potentially compromising the validity of the study itself, and requires critical evaluation of the impact on the study.
6.2 The final certification of a process validation study must indicate acceptance or rejection of the process parameters.
7. Laboratory
7.1 All laboratory tests, including D value determinations of microbial species must be performed by a competent laboratory that complies with regulatory requirements.
7.2 Laboratory tests must be validated and detailed methodology must be available in writing.
8. Equipment Qualification
8.1 Prior to commencing distribution and penetration of the sterilizing agent and biological challenge reduction studies, it is necessary that the equipment be checked and certified as properly equipped, installed and operating as per its design. Further guidance on conducting equipment qualification is available in the Validation Guidelines for Pharmaceutical Dosage Forms (GUI-0029).
8.2 Installation Qualification
The installation qualification must include verification of requirements for all the construction materials, the sizes and tolerances of the equipment, support services, power supplies, the alarm systems, monitoring systems with response tolerance and accuracy requirements, and the operational parameter requirements as governed by the established specifications.
8.3 Operational Qualification
Operational qualification must consist of three or more test runs demonstrating that controls, alarms, monitoring devices and operation indicators function properly; chamber conditions and integrity are maintained; written procedures accurately reflect equipment operation; and operation parameters are attained as pre-set for each test run.
9. Equipment Calibration
9.1 The range, sensitivity, accuracy, reproducibility, and response-time of all controlling, monitoring, and recording equipment must be adequate to demonstrate that defined process conditions are met.
9.2 All equipment must be calibrated and/or certified before any process validation can be performed. The standards used for calibration must be traceable to an appropriate standard. Documented evidence must be available for equipment calibration.
9.2.1 Sterilization by Moist Heat and Dry Heat
Equipment common to heat sterilization processes include temperature recorders and sensors, thermocouples, pressure sensors for jacket and chamber pressure, timers, conductivity monitors for cooling water, flow metres for water/steam, water level indicators, thermometers including those for thermocouple reference, and chamber monitoring.
9.2.2 Sterilization by Irradiation
Equipment common to both electron beam and gamma radiation processing technologies include dosimeters, spectrophotometers, thickness gauges, timers and recorders.
9.2.3 Sterilization with Ethylene Oxide and other Gases
Equipment common to gas sterilization include recorders, thermocouples, pressure sensors, timers, gas analysers, and balances.
9.3 Re-calibration must be performed as required and documented after any significant equipment maintenance.
10. Facilities
10.1 All facilities using terminal sterilization processes must meet conditions described in the Good Manufacturing Practices Guidelines (GUI-0001). Additional considerations are described below as applicable.
10.2 Facility Qualification for Sterilization by Irradiation
Prior to commencing any studies it is necessary to qualify the facility. The facility qualification focuses on the design, installation, and operation.
10.2.1 Facility Design and Installation
Qualification begins with the establishment of design, and installation requirements.
10.2.1.1 Design: Included in these written requirements are : the key construction materials, the source of ionizing radiation, product transportation system through the irradiator, support services and power supplies, control systems, monitoring and alarm systems with response tolerance and accuracy requirements, and performance specifications. All of these requirements must be compatible with the product, the product format, and the established process specifications.
10.2.1.2 Commissioning of the facility should be based on a written procedures that ensures design changes are documented in the "as built/as installed" drawings and in all manuals, and that the performance specifications are met.
10.2.1.3 All design/installation parameters should be documented and certified prior to operational qualification of the equipment.
10.2.1.4 Modifications must be documented as being performed according to predetermined requirements and certified as rendering the facility suitable for use.
11. General Considerations Prior to Process Validation
11.1 The product definition, in terms of physical, chemical, microbial and pharmacological properties should be established prior to validation.
11.2 Studies should be completed to determine bioburden in the materials to be sterilized. These studies should also include evaluation of the impact of hold times on the bioburden.
11.3 Specifications for raw materials and packaging components should be established.
11.4 The required SAL should be determined based on the use of the items being sterilized.
11.5 The compatibility of the sterilization process with the items to be sterilized should be evaluated.
11.6 Validation of analytical methods should be complete with adequate calibration and qualification of measuring equipment used in analytical methods and measurement of process parameters in operation of the sterilization cycle.
11.7 Indicating devices used in the validation studies or used as part of post-validation monitoring or requalification must be calibrated.
11.7.1 Physical and chemical indicators must be tested to demonstrate adequate pre-determined response to both time and exposure. Detailed written test procedures and records of test results must be available. The indicators must be used before a written expiry date and stored to protect their quality.
11.7.2 Biological indicators must be tested according to detailed written procedures for viability and quantitation of the challenge organism and for the time and exposure response. This applies to indicators either prepared in-house or obtained commercially.
11.7.3 For commercial indicators, a certificate of testing for each lot indicating the "D" value of the lot must be available. The quantitation is acceptable if the biological indicator manufacturer's count has been qualified and periodically confirmed as per written procedures.
11.7.4 Records of the testing for the biological indicators must be available. The biological indicator must be used before expiry and adequately stored.
11.7.5 When qualifying commercial or in-house biological indicators the choice of media (pH, electrolytes, carbohydrates, etc.) and sample carriers (suspension in ampoules, paper strips, inoculated products and inoculation on solid carriers) must be consistent with the materials used in the terminal sterilization process.
11.8 Sterilization Cycle Development
Two basic approaches are employed to develop sterilization cycles for terminal sterilization processes: Overkill and Probability of Survival. Microbial performance qualification may be required prior to introduction of new or altered products or when there are changes in packaging, loading patterns, equipment, process parameters, or bioburden based on seasonal variation or routine monitoring.
11.8.1 The Overkill method is used when the product can withstand excessive exposure to the sterilization process without adverse effects
11.8.2 The Probability of Survival approach is used when there are limitations to exposure to the sterilization parameters. In this approach, the process for the terminal sterilization is validated to achieve the destruction of the pre-sterilization bioburden with a minimum safety factor of an additional six-log reduction (1x10-6). The probability that any one unit is contaminated is therefore no more than one in a million; this is considered to be an acceptable level of sterility assurance.
11.8.2.1 The probability of survival is determined using a semi-logarithmic microbial death curve, where a plot of the log of the number of survivors versus time at a fixed exposure yields a straight line. After the line has crossed below 10o (less than one survivor), the y-value corresponding to a given time value is expressed as the probability of survival.
11.8.2.2 The determination of the minimum "F" value for the Probability of Survival approach is based upon the number of microorganisms (bioburden) found in a given product and when applicable their heat resistance.
12. Biological Challenge Reduction Studies
12.1 The sterilization cycle is assessed by introducing a known quantity of specific microorganisms with established "D" values and assessing the level of reduction with time. A probability of survival of 1 in 106 is confirmed in all cases.
12.2 The level of biological challenge selected for the study should consider product lot-to-lot variation in the bioburden (species and number).
12.3 A worst-case bioburden challenge using an appropriate organism as described within the below table is acceptable. In all other cases the microorganism with the highest Dvalue, occurring in the natural population as determined by sampling of the environment, should be used.
Table 1: Organisms for Biological Challenges
12.4 The level of biological challenge selected for the study should consider seasonal as well as lot-to-lot variation in the product bioburden (quantity) and "D" value.
12.5 Positive controls should be run with each load to verify the viability of the challenge organism.
12.6 The biological challenge may be run in conjunction with distribution studies/penetration studies.
12.7 The placement of biological challenges must be defined in writing. The challenge should be located as close as possible to the Dmin position and placed as close as possible to any sensors if run concurrent with distribution studies/penetration studies. The challenge should be placed in containers where practicable, so as to reflect the desired processing conditions.
12.8 A minimum of three cycles should be performed for each load configuration under evaluation.
12.9 Records of the organism type, Dvalue, challenge level, lot number, placement, and growth result should be available.
12.10 Growth of any challenge following any of the runs indicates that sterilization has not been achieved. In such cases, the process parameters must be evaluated. If no processing error is discernable, the sterilization process must be considered unacceptable.
12.11 When documented change control evaluation indicates a potential adverse effect on the sterilization method, the biological challenge studies should be repeated.
13. Process Validation: Sterilization by Moist Heat
13.1 Introduction
The Inspectorate recognizes that terminal moist heat sterilization, when practical, is presently considered the method of choice to ensure sterility. For the purpose of ensuring sterility, all aqueous-based sterile products intended to be sterile, should be subject to terminal moist heat sterilization except for instances where;
13.1.1 Terminal moist heat sterilization is not practical such as product or packaging degradation. Such instances of degradation are to be fully evaluated and documented.
13.1.2 Validated aseptic processes that exclude human intervention such as robotics, form-fill-seal and barrier systems (isolators).
13.2 "F0" and "D" Values
13.2.1 "F0" is the amount of time in minutes, equivalent to time at 121oC, to which a unit has been exposed during a sterilization cycle.
13.2.1.1 One method of calculating the "F0" is to integrate the time the unit is exposed to heat in terms of equivalent time at 121oC.
13.2.1.2 A second method is based on data obtained by the use of calibrated biological indicators.
13.2.2 The "D" value is the time, in minutes, required to reduce a microbial population by 90% (one log value) under specified test conditions (i.e. fixed temperature, single species, specified medium, etc.). When heat labile products will not withstand excessive heat treatment, "D121" value studies of product isolates are necessary to determine the minimum Lethality Factor (F0) that will provide an acceptable assurance of sterilization. Bacillus stearothermophilus is recognized as one of the most heat resistant microorganism and is commonly used for calculating "D" values in moist heat sterilization.
13.2.3 The minimum "F0" value required by a process can be related to the "D" value of the bioburden by the following equation:
F0 = D121 × (log A - log B)
where:
"D121" is equal to the time required at 121oC to reduce the population of the most heat resistant organism in the unit by 90%;
"A" is the microbial count per container; and
"B" is the maximum acceptable probability of survival (1 x 10-6 for pharmaceutical dosage forms).
13.2.4 Laboratory studies which determine the number and resistance of microorganisms associated with a product (bioburden) serve as the basis for calculating the required minimum "F0" value required for sterilization.
13.2.5 A more conservative approach assumes a "D121" value of 1 minute ("D" value of a highly heat resistant spore forming organism such as Bacillus stearothermophilus) for the bioburden of the product.
13.3 Heat Distribution Studies
Heat distribution studies are performed in order to determine temperature variation throughout the sterilizer chamber and should be performed prior to heat penetration studies. These studies should encompass empty chamber and loaded chamber evaluation and should be performed according to written procedures using temperature measuring sensors or probes which have been calibrated before and after use for each run.
13.3.1 The temperature uniformity requirements based on the type of sterilizer and specific processing parameters should be specified.
13.3.2 Empty Chamber heat distribution runs may be performed during equipment operational qualification. These runs should be performed using the maximum and minimum cycle times and temperatures specified for the equipment.
13.3.3 Test runs should be repeated at each pre-set cycle time and temperature required in the operational qualification protocol, in order to identify the heat distribution pattern of the empty chamber, including the slowest heating points. The studies should demonstrate that the uniformity of the sterilizing medium throughout the empty chamber is within the temperature variation limits established in the protocol.
13.3.4 Multiple temperature probes must be used in each test run. Simultaneous data recording must be available to sense each individual probe at specified time intervals in order to permit determination of the slowest and fastest heating zones in the chamber. The location of each these probes must be documented. These probes must be placed in a manner to demonstrate a uniform temperature distribution throughout the sterilizer chamber.
13.3.5 The data from all runs must be collated into a temperature profile of the chamber.
13.3.6 Loaded chamber heat distribution studies must also be performed using maximum and minimum chamber load configurations to represent various products and packaging configurations with consideration to the following:
13.3.7 Multiple temperature probes are placed throughout the chamber but not inside the units of the load to determine the effect of any defined loading pattern on the temperature distribution within the chamber.
13.3.8 The test runs of a sterilization cycle should be performed using the different container sizes to be processed using the sterilization parameters specified for the normal production process.
13.3.9 The position of each temperature probe in each test run must be documented.
13.3.10 The slowest heating point(s), or cold spot(s), in each run must be determined and documented.
13.3.11 A minimum of 3 repeat runs must be performed to establish whether, for a given load configuration, the location of the cold spot(s) is fixed or variable.
13.3.12 A temperature distribution profile for each chamber load configuration should be developed and documented.
13.3.13 It must be demonstrated that all runs of a sterilization cycle consistently meet the specified criteria for acceptable temperature uniformity.
13.3.14 Each test run performed must be evaluated. The completed studies should be certified prior to beginning heat penetration studies.
13.4 Heat Penetration Studies
In order to verify that the sterilizing temperature has been reached throughout the load subjected to moist heat sterilization, it is necessary to conduct heat penetration studies. These studies are conducted to ensure that the coolest unit within a pre-defined loading pattern (including minimum and maximum loads) will consistently be exposed to sufficient heat lethality (minimum "F" value).
13.4.1 Heat penetration studies must be performed according to detailed written procedures using temperature sensing probes which have been calibrated before and after each validation runs. Simultaneous data recording must be available to sense each individual temperature probe within specified time intervals to permit determination of the slowest and fastest heating units in the chamber.
13.4.2 The validation protocol should make provision for such variables as container size, design, material, viscosity of solution and fill volume. The container should have the maximum fill volume of a solution with heating characteristics as slow as the slowest-to-heat solution sterilized by the specified cycle. Initial container temperature mapping studies should be considered depending on the container size.
13.4.3 Heat penetration studies must be conducted with the maximum and minimum loading configurations for each sterilization cycle using the sterilization parameters specified for the normal production cycles.
13.4.4 Heat delivered to the slowest heating unit of the load is monitored and this data is employed to compute the minimum lethality ("F" value) of the sterilization process. Once the slowest heating units of the load have been identified, at least three replicate runs should be performed to verify that the desired minimum process "F" value can be achieved reproducibly throughout the load. The process is considered acceptable once such consistency in lethality has been adequately established.
13.5 Biological Challenge Reduction Studies
13.5.1 Studies of biological challenge reduction as described in Section 12 are performed.
14. Process Validation: Sterilization by Irradiation
14.1 Introduction
Radiation processing, in the context of this guide, is considered to mean the exposing of the product to ionizing radiation (i.e. such as gamma radiation generated by an isotopic source such as Cobalt 60 radionuclides or Cesium 137 radionuclides, or to an electron or X-ray beams, or the photons generated from an electron beam generator machines) in a controlled manner to ensure that a pre-determined dose is delivered to the product.
There are significant differences between the two technologies which affect process validation. For instance, gamma radiation delivers a specified dose relatively slowly, (over a period of minutes to hours), to a large volume of product. Conversely, an electron beam generator can deliver the same dose in a fraction of a second to a very small volume of product. These and other factors make it imperative that a product be validated independently for each source of radiation. Radiation sterilization is used mainly for the sterilization of heat sensitive materials and products. In that many medicinal products and packaging materials are radiation-sensitive, this method is permissible only when the absence of deleterious effects on the material/product has been confirmed prior to use.
14.2 Product Qualification
14.2.1 A product qualification program demonstrates the effects of ionizing irradiation on the product. The most important outcome of product qualification is the determination of the product's Maximum Tolerated Dose (DmaxT) for the product. In addition the Maximum Process Dose (DmaxP) and the Minimum Process Dose (DminP) will also be set.
14.2.2 The DmaxT is that dose of radiation which induces an unacceptable change in the analytical profile of the pharmaceutical. It may be possible to select a radiation dose at which no radiation induced changes in the analytical profile can be detected. It is important in the initial product qualification steps to test the product using widely separated radiation doses. This will quickly assess the ability of the product to withstand radiation and to "zero-in" on the most appropriate radiation dose for further testing.
14.2.3 Prior to commencing any determination of DmaxT for the product, it is essential to determine if any of the components of the product have received prior radiation treatment. Radiation effects are cumulative. Therefore, any prior radiation treatment will affect the interpretation of dose-effect experiments. The effects of variations in density of the packages are also a consideration to be looked at.
14.2.4 The DmaxP for a product must not exceed its DmaxT. It is determined by judgment. It is usually set below the DmaxT to ensure that the product is not overexposed. It is dependant upon the product loading, and the physical parameters of the irradiator, such as source strength.
14.2.5 A third factor is the DminP. The DminP is determined by the product loading pattern, density, and the operating characteristics of the irradiator. The ratio of the DmaxP to the DminP is known as the Dmax/Dmin Ratio. This Ratio is the key to successful radiation processing.
14.3 Sterilization Approach
Three basic approaches can be employed to develop a sterilization process for radiation processing: Overkill, Bioburden-Based, and Species-Based Bioburden Sterilization.
14.3.1 The Overkill method has traditionally been used when the product can withstand radiation doses in excess of 25 kGy, without adverse effects. It is based on worst-case bioburden assumptions. Therefore product specific bioburden and resistance data are not required. The irradiator and product loading parameters are selected to assure that the product receives the DminP of 25 kGy and that the DmaxT is not exceeded.
14.3.2 The Bioburden-Based approach is well explained and detailed in the AAMI Guidelines. In using this approach, it is necessary to demonstrate that the pharmaceutical product's bioburden is similar in nature to that assumed for the AAMI calculations. This approach is only relevant in cases where the product's bioburden (before treatment) is consistent, and can be proven to be so. The result is a treatment dose that is tailored to the actual need (bioburden), and that is less than the very high (for pharmaceuticals) 25 kGy.
14.3.3 The Species-Specific Bioburden approach is more particularly suited to the pharmaceutical industry as it relates the radiation dose delivered to the most resistant organism in the bioburden population found in the manufacturing area. This population should be significantly skewed in the direction of radiation sensitive organisms, especially when dealing with aseptic processing areas. This should result in a much lower dose of radiation being needed to achieve sterilization. For this method to be effective it is necessary to conduct dose distribution studies to determine the product loading pattern which achieves the best possible Dmax/Dmin ratio.
14.3.4 Validation studies must confirm that the product in the Dmin position actually receives the minimum dose, and that the product in the Dmax position does not exceed the(DmaxP).
14.4 Dose Distribution Studies
Dose distribution studies are performed in order to detere the Dmax and D positions in the irradiator transport mechanism for the product in its predetered loading configuration; and to confirm that the radiation dose delivered to the product does not vary outside the process specification.
14.4.1 These studies must be performed according to written procedures using appropriately placed dosimeters which have been calibrated against a known standard.
14.4.2 The location of each dosimeter must be documented. The placement of the dosimeters must ensure that a uniform distribution is achieved throughout the transport/irradiation system.
14.4.3 The dosimeters must be capable of measuring the dose over the desired range.
14.4.4 The data from all runs should be collated into a dose-map profile for each product transfer/irradiation device.
14.4.5 Dose distribution studies must be performed for each different product loading configuration, and each product size.
14.4.6 The studies should prove that the dose uniformity requirements, as contained in the process specification, are consistently achieved.
14.4.7 Failure to demonstrate operational consistency within the chosen criteria for acceptable dose uniformity precludes the validation of the process. Each test run performed must be evaluated. The completed studies must be certified.
14.5 Product Loading Patterns
The configuration of the product in/on the transport mechanism for conveyance through the irradiator is critical to achieving the specified Dmax/D ratio and the specified doses which are essential to the maintenance of product integrity and the desired SAL. A detailed 'map' of how the product is to be placed in/on the transport mechanism forms a part of the process validation documentation. It is important to address the possibility of and effects of improperly loaded product.
14.6 Biological Challenge Reduction Studies
14.6.1 Studies of biological challenge reduction as described in Section 12 are performed to ensure that the product does not demonstrate a radioprotective effect on the microbial population.
14.7 "Cycle" Interruptions
14.7.1 For the Gamma Process
14.7.1.1 It is necessary to specify for each product, the maximum permitted length of time from the completion of the filling cycle to the commencement of the sterilization treatment. Normally, all of a production lot of a pharmaceutical would be simultaneously exposed to the gamma radiation source. (There will be some exceptions for larger volumes/bulkier drugs.) For products treated by electron beam, where each unit is individually exposed, this period would be from the start of processing the first unit until the last unit has been sterilized.
14.7.1.2 For mechanical, safety or operational reasons, the radiation source may need to be turned off during the course of a "treatment", thus interrupting the sterilization treatment. For those products which are capable of sustaining microbial growth, it will be necessary to define the maximum length of time permitted for an interruption in relation to the treatment received at the time of interruption. For example, for gamma radiation processing; if the interruption occurs before 50% of the dose has been delivered, and the interruption is of sufficient length to allow for microbial growth, then a procedure must be in place to define how the product will be handled; i.e. allowed to continue, to restart, or to reject. If more than 50% of the dose has been delivered then it may be permissible for the cycle to be continued as there would be insufficient bioburden to support growth. For electron beam processing; it will be necessary to detere if a particular unit was completely irradiated at the moment of shut down. The delay factor for the remaining units must have been defined.
[Comment: One could consider doing this work as part of the product qualification activity, if it was felt that a cycle interruption would be crucial to the successful sterilization of the product.]
14.7.2 For the Electron Beam Process
14.7.2.1 It is necessary to specify for each product the maximum permitted length of time from the completion of the filling cycle to the end of the irradiation treatment. This is because each unit within a batch (unit here can mean an individual vial or a carton), is sequentially exposed to the electron beam. Thus product unexposed could permit microbial growth, while awaiting treatment. Note the contrast here between gamma and electron beam processes.
14.7.3 For Both Processes
14.7.3.1 For both processes it will be necessary to have the appropriate procedures in place to direct the operator as to the appropriate person to contact in the event of a "cycle" interruption or a delay in the commencing/completion of the irradiation "cycle".
14.8 Temperature Control
14.8.1 For those products which are temperature-sensitive, it will be necessary to document the permitted temperature range of the product upon arrival at the irradiation facility and the time available for irradiation before the product temperature rises to the maximum tolerated level. It may be necessary to provide cooling of the product during the irradiation process. The manner in which this is to be done must be specified. This type of information will form part of the process validation documentation.
15. Process Validation: Sterilization by Ethylene Oxide and Other Gases
15.1 Introduction
Sterilization by Ethylene Oxide (EtO) is due to alkylation of sulphydryl, amino, carboxyl, phenolic and hydroxyl groups in spore and vegetative cells. It also causes a reaction with the nucleic acids of the bacterial cell.
Ethylene Oxide Sterilization depends on the following major parameters that influence sterilization: relative humidity, temperature, time at exposure and gas concentration. Design of sterilization cycles by EtO must also consider: product preparation; delivery of the sterilization parameters and removal of the residual sterilizing agents. Aeration may be performed within the sterilizer or in a separate area or both. Parameters monitored include vacuum/pressure levels, temperatures, time, steam and gas concentration, air washes and air flow.
Factors that influence sterilization include: bioburden, packaging, package density, product/ package loading patterns; pre-cycle conditioning, gassing and evacuation times, exposure to relative humidity, exposure temperature, EtO gas concentration.
Primary packaging must be able to tolerate cycle parameters while maintaining product and package/ container integrity for the expected life of the product. Consideration must be given to the influence of EtO sterilant to the product sterility due to moisture absorption or glycol formation. Inadequate package design may lead to problems. These problems are caused by use of non-porous materials; attachment of labels with large surface areas to breathable materials; use of plastic or foam inserts/ supports; application of moisture resistant coatings.
Choice of packaging materials should include consideration of its resistance to chemical and physical changes during the sterilization process such as: physical strength and permeability. The sterilizing gas must not affect the product integrity, such as the causing of cracking, phase separation and bio- compatibility. Product design should avoid resistance of EtO penetration such as use of pressure relief valves, stop corks, manifolds, cotton plugs which restrict EtO penetration; application of bleaching agents that contain free chlorine which react with EtO Ethylene Chlorhydrate or Ethylene Glycol.
Any changes to primary or secondary packaging or in package or case configuration or case composition may have an impact upon the sterilization of the product and will require re-validation.
EtO may be used as a pure gas (100%) or in a mixture of gases such as carbon dioxide or nitrogen. During EtO sterilization cycle development and validation studies, biological indicators should be tested as soon as possible after exposure to the sterilization cycle because microbial inactivation continues after completion of the sterilization cycle due to the presence of EtO residues.
15.2 EtO Sterilization Parameters
15.2.1 Relative Humidity: Maintaining a wet atmosphere in the sterilization chamber increases the effectiveness of the EtO sterilization by increasing EtO penetration through cell walls. A relative humidity of about 35 % is desirable as it has been demonstrated to be beneficial for effective EtO sterilization. Increased humidity can cause the formation of condensation on the product, the chamber walls, and optical EtO sensors. Products and materials sterilized using cycles with relative humidity of less than 30 % are known to have an increased microbiological resistance. Products and materials processed in cycles that contain 30 to 70 % relative humidity are known to have a linear microbiological resistance.
15.2.2 Temperature: EtO cycle effectiveness improves as the temperature increases. The temperature in the chamber must be high enough to prevent the EtO from liquefying. Product tolerance for the required high temperatures must be considered.
15.2.3 Gas Concentration: the higher the EtO level the more effective the sterilization process and requires a lesser dwell time. As the EtO gas concentration increases from 50 to 500 mg/ L, the inactivation rate increases. At a level higher than 500 mg/ L the inactivation rate is not as pronounced.
15.2.4 Diffusion: the higher the diffusion rate of EtO from the chamber to the product in the load the shorter the required dwell time. Diffusion is improved by creating a vacuum in the chamber before it is charged with EtO.
15.2.5 Time: the exposure of the product at temperature and defined EtO gas concentration during EtO exposure
15.3 Design Of EtO Sterilization Cycles
There are three traditional approaches in the design of EtO sterilization cycles:
15.3.1 Overkill cycle : This is the most common cycle. The cycle is developed by performing fractional cycles to establish the survivor curve to demonstrate a log 100 with biological indicators and product samples. The exposure time is then doubled to provide the overkill sterilization process. Thereafter routine bioburden monitoring should be performed.
15.3.2 Biological indicator (BI)/ Bioburden cycle : This sterilization process involves the use of a microbial challenge population lower than 106. However, the challenge population should be not less than 103. Bioburden testing is performed to ensure the challenge organism is more difficult to kill than the bioburden. Bacillus subtilis Var. Niger is commonly used for the purpose of EtO sterilization because of its high resistance. The BI should be distributed throughout the product load and in the same orientation. The placement should include spots that present the greatest challenge to the sterilization cycle.
15.3.3 Absolute Bioburden cycle: This cycle is used when the product bioburden by nature of its location on the product, the natural resistance, or the population level or any combination of these items may require the use of absolute product bioburden to monitor the sterilization process because of resistance. Routine bioburden monitoring is required.
Cycle development includes exposing representative samples to incremental exposures and testing the exposed samples for recovery of survivors and performing counts. The more resistant organisms are isolated and used in EtO cycle development studies and an inactivation curve is established. The inoculums should consist of the bioburden average plus three standard deviations (3σ).
15.4 Validation Of EtO Sterilization Cycles
The following are additional consideration to be made in the Validation of an EtO Sterilization Cycle.
15.4.1 Determination of rates of dissipation of the three major residues after being subjected to the EtO sterilization cycle.
15.4.2 The maximum allowable levels of Ethylene Oxide (EtO) residues on drug products must be specified. These limits must be based on safety studies and on published international safety standard. Provisions for the routine monitoring of the levels of EtO, ethylene chlorohydrin (ECH), and ethylene glycol (EG) on drugs, drug products, and biological products must be in place.
15.4.3 Validated analytical methods for the determination of EtO, ECH and EG residues
15.4.4 Validation of gaseous sterilization procedures should involve additional considerations such as determination of time and humidity in the preconditioning area, temperature, pressure, time and humidity in the chamber, ventilation of load after sterilization, the method used to recover the challenge spore, the incubation period of the exposed spores.
15.5 Sterilization With Vapor Phase Hydrogen Peroxide (VHP)
15.5.1 The two approaches for the use of vapor phase hydrogen peroxide (VHP) are:
15.5.1.1 A deep vacuum to pull liquid hydrogen peroxide (30%) from a cartridge through a heated vaporizer and into the sterilization chamber. This process usually operates at temperatures of 55oC to 60oC
15.5.1.2 A flow- through approach, in which the vaporized hydrogen peroxide is brought into the sterilization chamber by a carrier gas.
15.5.2 Although vapour phase hydrogen peroxide (VHP) systems meet several of the criteria for an ideal sterilization technology, they cannot be used with highly absorptive materials such as cellulosic materials, nylon and certain types of rubber. Polypropylene and polyester packaging are known to retain hydrogen peroxide residues, necessitating post-sterilization aeration.
15.5.3 The effect of residual VHP on microorganism recovery when performing surface and air monitoring should be known.
15.5.4 VHP is used mainly in surface sterilization such as in flexible and rigid isolators, pass-throughs, production filling lines, biological safety cabinets and clean rooms. Its use in terminal sterilization of pharmaceutical dosage forms is very limited.
16. Post Validation Process Monitoring
16.1 The sterilization process must be monitored routinely to ensure that the process conditions are routinely met as specified. These results should be documented in the processing records.
16.1.1 The requirement for, the existence of, and adherence to effective, routine process-monitoring procedures should be included in the validation protocol.
16.1.2 Biological challenges should be documented when performed in routine process monitoring procedures. The location, number, type and lot number of the challenge must be included in the records along with the actual test results.
16.1.3 Deviations from defined processing conditions must be documented, investigated and assessed regarding the impact on the product, and on process objectives. In the absence of qualified evaluators, the sterilization process should automatically be considered to have been compromised.
16.2 For sterilization approaches based on either of the two Bioburden-Based methods, samples for ongoing bioburden testing and data collection should be obtained from each batch of drug product for an initial period of time sufficient to define the limits of species and number of organisms for seasonal/operational variations to be adequately documented and controlled.
17. Requalification and Revalidation
17.1 All changes to the equipment, sterilization system, sterilization or process parameters, and primary packaging components must be pre-authorized through the Change Control Procedure or be required as part of a pre-established maintenance program. The HPFBI guidance document Validation Guidelines For Pharmaceutical Dosage Forms (GUI-0029) provides additional information relating to the requalification requirements.
