The isolator system must be validated before its use in sterility testing as part of a batch release procedure. To verify that the isolator system and all associated equipment are suitable for sterility tests, validation studies are performed in three phases: installation qualification (IQ), operational qualification (OQ), and performance qualification (PQ). The following sections contain points to consider in the validation of isolator systems for sterility testing. The assignment of test functions to a particular phase of the validation program (i.e., IQ, OQ, and PQ) is not critical, as long as proper function of the isolator is demonstrated and documented before its use in compendial Assays.
Installation Qualification (IQ)
The IQ phase includes a detailed description of the physical aspects of the system, such as the dimensions, internal configuration, and materials of construction. The unit layout is diagrammed with interfaces and transfer systems clearly and dimensionally indicated. Compliance with design specifications for utility services, such as air supply, vacuum, external exhaust, and temperature and humidity control, is verified. Other equipment used with the isolator system is also described in detail; if any revisions to design specifications are made, these are included. Equipment manuals and copies are catalogued and stored where they can be retrieved and reviewed. Compliance of drawings to design specifications is verified. All drawings and process and instrumentation diagrams are catalogued, and stored and are retrievable.
All documentation is reviewed to verify that it precisely reflects the key attributes of the installed system. This establishes a general benchmark for the isolator system's compliance with design specifications and installation requirements.
Potential process-control or equipment problems that could cause system failure during operation are identified and documented during failure-mode analysis and hazard analysis. The system is modified, if necessary, to minimize the risk of failure, and critical control point methods are established.
The results of the IQ are summarized in an Installation Qualification Report. The following documentation is suggested.
The equipment is listed with its relevant design specifications. The IQ Report verifies that equipment meeting the appropriate design specifications was received and that it was installed according to the manufacturer's requirements.
The construction materials of critical system components are checked for compliance with design specifications. The compatibility of the intended sterilization method with the construction materials is verified.
System instruments are listed with their calibration status.
All utilities required for operationas defined in the operating manuals and process and instrumentation diagramsare checked for availability and compliance with design specifications. Any connection between utility systems and the isolator system is inspected, and conformance of these connections to specifications is verified.
HEPA filters and other microbial retentive filters are tested and certified; copies of test results and certificates are included in the IQ Report. Purchase orders are reviewed, and conformance of the air filtration system to specifications is verified.
All computer software associated with the isolator system is listed with its name, size, and file revision number. The master computer disks are checked for proper labeling and are stored securely.
Operational Qualification (OQ)
The OQ phase verifies that the isolator system operates in conformance to functional specifications.
Operational Performance Check
This test verifies that all alert and alarm functions comply with their functional specifications. The system's ability to comply with all set points and adjustable parameters is verified.
Isolator Integrity Check
The integrity of the isolator is maintained during all normal operating conditions. A leak test is performed to verify compliance with the manufacturer's functional specifications and to ensure safety prior to charging the isolator with a sterilizing chemical. To safeguard against adventitious contamination, isolators are operated at a positive pressure differential of about 2050 Pa during normal operation. If constant overpressure is needed, validation studies must show that the set point can be maintained and controlled during operation.
Sterilization Cycle Verification
A sterilization cycle is performed to verify that all actual values conform to cycle steps and set points.
Different sterilization methods can be used to eliminate bioburden from isolator systems and supplies. Among the chemicals that have been used to treat isolators are peracetic acid, chlorine dioxide, ozone, and hydrogen peroxide; each has different requirements for exposure conditions and process control. It is critical to comply with the manufacturer's operational requirements for the selected sterilization method and to describe them in the functional specifications. Temperature and humidity control within the room is critical when hydrogen peroxide vapor is used in sterilization. The temperature inside the isolator is also important, particularly for hydrogen peroxide vapor sterilization, where it is critical to maintain the concentration below the condensation point. Some sterilization chemicals, such as chlorine dioxide and ozone, require the addition of moisture to the isolator prior to sterilization. When elevated relative humidity is required, the ability to control it must be verified during OQ.
It is also important to verify the concentration and distribution of the sterilizing chemical. When applied in gaseous or vapor form, the concentration is measured using chemical indicators, spectroscopic methods, or electronic sensors. Distribution may also be tested using chemical indicators. [NOTEChemical indicators provide qualitative, but not quantitative, information.]
Gas and vapor sterilization methods require fans in the isolator to distribute the chemical evenly. The location and orientation of these fans are adjusted to ensure optimum air distribution. Since shelving units, equipment, glove-and-sleeve assemblies, and half-suits have an effect on distribution patterns, distribution checks are done with the isolator fully loaded with equipment and supplies, and the setup of these units is defined and documented.
Many installations use smaller transfer isolators as portable surface sterilization units. In these transfer isolators, test articles and supplies are treated chemically to eliminate bioburden before transfer through an RTP into the testing isolator. Its loading configuration is defined, and configuration drawings are reviewed and verified during the OQ. [NOTEThe sterilizing chemicals used in isolators work on the surfaces of materials; therefore, any surface that is occluded will not be treated and could contain viable bioburden.]
Sterilization agents need to be removed from the isolator after the exposure period, which is accomplished by a current of fresh air provided either by the sterilization equipment or by some other means. Aeration is accomplished either in an open loop, in which the gas is exhausted through a vent to the atmosphere, or in a closed loop, in which the chemical is removed and destroyed by the sterilization equipment. The aeration system is checked; if an open-loop configuration is used, the external exhaust system's flow and safety are checked.
Sterilization Cycle Development
When the OQ is completed, sterilization cycle development is performed to establish the parameters necessary for process control during routine sterilization cycles. Any of the methods generally used in the industry for the validation of sterilization processesincluding bioburden-based and overkill methodsare adequate. The sterilization process is challenged with biological indicators (BIs). The spore population and resistance of the BIs to the sterilization conditions being applied is known. Wherever possible, a true D value is obtained for the BI system (see Biological IndicatorsResistance Performance Tests 55
); it is acceptable to obtain the D value from the BI vendor. When it is impossible to determine an accurate D value and no means to verify the concentration of the sterilizing agent is available, the half-cycle approach to cycle development and verification is employed.
Performance Qualifications (PQ)
The PQ phase verifies that the system is functioning in compliance with its operator requirement specifications. At the completion of the PQ phase, the efficacy of the sterilization cycle and, if appropriate, the adequacy of sterilizing chemical venting are verified. All PQ data are adequately summarized, reviewed, and archived.
In general, cleaning is not critical for sterility testing applications. However, residual products are a concern in multiproduct testing, particularly for aggressive antimicrobial agents, since these materials could interfere with the ability of subsequent tests to detect low levels of contamination in the product. Concerns about contamination with the product are heightened when it is an inherently antimicrobial powder, since powders are more readily disseminated. Cleaning to a level at which no visible contamination is present is adequate for sterility test isolator systems and is a suitable operator requirement specification. The cleaning method, frequency, equipment, and materials used to clean the isolator are documented.
The interior surfaces of the isolator, the equipment within the isolator, and the materials brought into the isolator are treated to eliminate all bioburden. The sterilization of isolator surfaces, sterility testing supplies, and test articles is different from the sterilization of product contact parts or drug components used in product manufacturing. The methods used to sterilize an isolator may be able to achieve log reduction values typical of production overkill processes. This level of insurance of sterility cannot be guaranteed over time. Upon completion of the sterilization process, asepsis within the isolator is maintained primarily by the air filtration system, by the appropriate materials transfer operations, and, most importantly, by the integrity of gloves used to conduct aseptic manipulations.
The sterilization methods used to treat isolators, test articles, and sterility testing supplies are capable of reproducibly yielding a six-log kill against an appropriate, highly resistant biological indicator (BI; see Biological Indicators for Sterilization 1035
), as verified by the fraction negative or total kill analysis methods. Total kill analysis studies are suitable for BIs with a population of 104
spores per unit, while fraction negative studies are suitable for BIs with a population of 105
or greater. A sufficient number of BIs are used to prove statistical reproducibility and adequate distribution of the sterilizing agent. Particular attention is given to areas that pose problems relative to the concentration of the agent. A larger number of BIs are used in isolators that are heavily loaded with equipment and materials. Also, when it is not possible to use one or more calibrated sensors to directly measure the concentration of the sterilizing agent, the placement of additional BIs is considered. The ability of the process to reproducibly deliver a six-log kill is confirmed in three consecutive validation studies.
The operator establishes a frequency for resterilization of the isolator. The frequency may be as short as a few days or as long as several weeks, depending on the sterility maintenance effort (see Maintenance of Asepsis within the Isolator Environment).