1209 STERILIZATIONCHEMICAL AND PHYSICOCHEMICAL INDICATORS AND INTEGRATORS
The Federal Code of Regulations, Part 211 on Good Manufacturing Practices for Finished Pharmaceuticals in section 211.165 states: There shall be appropriate laboratory testing, as necessary, of each batch of drug product required to be free of objectionable microorganisms. This statement has been interpreted to mean that an alternate laboratory control test for sterility is required for any batch load of a product that is parametrically released. An appropriate laboratory test for each batch may be a biological indicator, which is included in each batch of product that is terminally sterilized (see Biological Indicators for Sterilization 1035), or a physicochemical indicator or integrator. This requirement may also be met by a primary product release system that includes the documented recording of thermometric measurements systems that are calibrated with a NIST traceability system and that demonstrate a ±0.5 performance capability.
The presence of this chapter in the USP does not mean that chemical indicators and integrators are primary release requirements for parametric released product. The recorded and documented measurements from established thermometric measurement systems and associated process controllers (that have been calibrated and used during initial and periodic validation studies, as well as in routine production) can be considered to be primary, product-release systems for parametric release.
Performance standards within lots and between lots of physicochemical indicators or integrators from a given manufacturer should be consistent. They should not interact physically or chemically with any container or product when placed adjacent to the product for sterilization in the sterilizer load, and should not alter the strength, quality, or purity of the sterilized article. The safety of personnel handling the physicochemical indicators or integrators should also be assessed, and, if need be, appropriate precautions should be taken.
Similar to biological indicators, chemical indicators are considered Class II devices and require the indicator manufacturer to obtain a device 510K approval prior to commercial use.
Recorded process engineering data can be supplemented by the presence in each sterilized batch of a physicochemical indicator. A physicochemical indicator is defined as a device that responds in a measurable fashion to one or more critical sterilization parameters.
A number of different kinds of indicators dependent on chemical or physicochemical means have been developed for monitoring sterilization cycles. Some products are used in a sterilization apparatus for monitoring whether the contents have been exposed to a selected factor (i.e., temperature) of the particular sterilization cycle, but may not show the duration or intensity of such exposure. Chemical and physicochemical indicators are used to monitor a physical parameter of a sterilization apparatus and can be placed on the outside of the packages of articles to be sterilized, or they may be distributed within the sterilizer load. In the latter case, one can evaluate to some extent the effect of the packaging material and configuration of the load on the selected parameter.
A physicochemical integrator is defined as a device that responds to a sterilization process critical parameter, which results in a measurable or quantifiable value that can be correlated to some standard of microbial lethality. Physicochemical integrators have been designed to broadly match the predictable inactivation of those spore preparations in biological indicators that have high and defined resistance to the sterilizing agent.
The manufacturers of physicochemical integrators should provide data to demonstrate that the labeled performance characteristics tests of the integrators are met. Users of physicochemical integrators should verify that specific measured values directly correlate to successful microbial lethality in a validated sterilization cycle.
A physicochemical integrator indicates whether or not the critical combination of physical parameters of a validated sterilization cycle has been met or exceeded. The integrator is not generally used as a substitute for a biological indicator in the development and validation of sterilization cycles. An indication by a physicochemical integrator that the critical combination of physical parameters of a stated sterilization cycle has been achieved should not be considered equivalent to the inactivation of spores of a variety of biological indicators. However, the physicochemical integrator can detect whether the sterilization process has been continued for too long, at too high a temperature or gas concentration, or has been overexposed to radiation.
The interval between the lower range and the upper range of time, or any other designated set of parameters, resembles the survival time and kill time window characteristics of a biological indicator. This interval should not be wider than that desirable for the designated parameter, but may be narrower if the manufacturer is able to achieve consistent performance over a narrower range. Even where a sterilization apparatus with consistent performance is used, cases may occur where the determined performance characteristics of the integrator differ from the label claims. This could represent a difference between the user's apparatus performance and the manufacturer's apparatus used for verifying the label claims. Closer conformity to the label claims may also be shown with any highly developed apparatus, such as a BIER vessel.1, 2 Hence, the integrator requires its own precautions in use and has appropriate interpretive criteria within its performance characteristics. Tests for performance characteristics of physicochemical integrators include determination under applicable defined conditions of (a) the maximum time of exposure at which none of the specimens indicates that adequate exposure to the cycle has occurred, and (b) a minimum time of exposure at which all specimens show that adequate exposure to the cycle has occurred. An intermediate time of exposure, where about half the number of specimens show adequate exposure, could indicate an approaching exposure endpoint for the physicochemical integrator.
Because an indicator reflects only the interaction of the physical parameters of sterilization, it will not be affected by some of the factors that may influence the resistance of the microbial load on the products to be sterilized (e.g., progeny resistance, spore population, inoculum substrate, oil, salts, proteins, or residues or configurations), all of which may protect a contaminated area from penetration by the sterilizing agent. (Hence, the inappropriateness of these devices for cycle development.) There are other factors, however, that may affect a biological indicator that could also affect a physicochemical integrator (e.g., interfering configuration of a pack in which the integrator was placed, variations in the applied timing or temperature control, or failure of the apparatus to reach the set temperature or meet other requirements).
Defective performance of the sterilization apparatus generally can be ascertained from gauges and from records of temperature, pressure, time of exposure, and gas concentration, whichever are applicable. The integrator can only indicate inadequate, adequate, or excessive exposure to a combination of critical sterilization parameters. Where an integrator shows inadequate exposure to the sterilization parameters, it is necessary to ascertain whether the gauges and recordings reflect accurately the sterilization conditions within the sterilization chamber. Variations between sterilization vessels, which might affect the efficiency of a selected sterilization cycle, might be detectable by parallel exposure of several integrators in a number of locations in each sterilizer load.
Physicochemical integrators for steam sterilization are designed to react predictably to a particular combination of physical sterilization parameters: temperature, steam pressure, and time of exposure. Deviation to some extent of one or more of these critical parameters, not compensated by modification of other parameters, causes the integrator to indicate failure to reach the preset integrated limits.
Physicochemical integrators for ethylene oxide sterilization are designed with similar general principles as the integrators for steam sterilization, but to react predictably to the particular combination of the physical sterilization parameters: humidity, temperature, sterilizing gas concentration, and time of exposure. Deviation to some extent of one or more of these critical parameters, not compensated by modification of other parameters, causes the integrator to indicate failure to reach the preset integrated limits.
Physicochemical integrators have been designed to match broadly the predictable inactivation of spore preparations that have a high and defined resistance to the sterilizing agent. For steam sterilization, a strain of Bacillus stearothermophilus is used (see Biological Indicator for Steam Sterilization, Paper Carrier), and for ethylene oxide sterilization, a strain of Bacillus subtilis, subspecies niger, is used (see Biological Indicator for Ethylene Oxide Sterilization, Paper Carrier). Since there are no standard preparations of these strains, the performance characteristics of these physicochemical integrators must be interpreted in relation to a specific validated sterilization cycle.
Performance standards within lots and between lots of physicochemical integrators from a given manufacturer should be consistent. The integrators should not interact physically or chemically with container or product when placed adjacent to the product for sterilization in the sterilizer load, and shall not alter the strength, quality, or purity of the sterilized article beyond official requirements. Users should obtain information from integrator manufacturers on whether or not sterilization in the presence of physicochemical integrators may affect particular articles to be sterilized. In addition, safety in using these integrators should be verified.
Moist Heat Sterilization
The use of steam sterilization physicochemical integrators to supplement the information obtained through physical assessment of the critical operating parameters should be part of parametric release of moist heat sterilized products. These should be designed to enable the assurance that the lethality delivery specified for the process has been met or exceeded. The consistency of the performance of physicochemical integrators for moist heat sterilization should be ensured through the testing of performance characteristics that include testing of the performance of the indicator or integrator system at various pre-set selected moist heat process conditions.
Critical elements of this type of physicochemical integrator would include an organic compound sensitive to the combination of temperature and steam, a polymeric material penetrable by saturated steam, and a wicking device under the polymeric material that is in contact with the organic compound. As steam passes through the polymeric material, the organic compound melts in a predictable fashion in steps dependent on the steam temperature during the cycle. The liquefied material travels along the wick for a distance that can be measured on a scale. This organic compound has a stated melting temperature range. Some integrators may, for example, have melting ranges of 132.2 to 134.5 or of 137.0 to 142.0. Other melting ranges could also be specified so as to indicate the sterilization parameters to which it has actually been exposed. The combination of the sterilization parameters, applied for the exposure time required for a stated moist heat sterilization cycle, is indicated on the front of the article by the linear travel of the melt.
These types of physicochemical integrators can also be used for so-called flash moist heat sterilization cycles in which the successive steps of the sterilization process are rapidly carried out in such a manner as to achieve the required lethality for the validated process. Other types of physicochemical integrators for moist heat sterilization can be used if they are also calibrated against a specified validated moist heat sterilization cycle.
Ethylene Oxide Sterilization
Physicochemical integrators for ethylene oxide sterilization should be designed to match broadly the predictable inactivation of spore preparations that have a high and defined resistance to ethylene oxide sterilization. The inactivation of spores of a strain of Bacillus subtilis, subspecies niger, can be used as a model, although other spores of relevant microorganisms can also be used. The critical elements of physicochemical integrators for ethylene oxide sterilization are a base with an organic compound along a linear indicator strip sensitive to a combination of temperature, humidity, and sterilizing gas concentration. Where the organic compound is exposed to a sterilizing gas mixture at a specific temperature and humidity, a chemical reaction triggers the appearance of a color along the linear indicator bar. This is dependent on the time of exposure under the conditions of ethylene oxide sterilization in a predictable fashion. The absence of fading or of decolorization of the indicator bar for a stated period after the sterilization cycle has been completed would confirm adequate humidification in the cycle. The integrator should be capable of detecting deviations from the prescribed parameters of temperature, sterilizing gas concentration, humidity, and time of exposure that may affect sterilization. It does not show the required reactions if exposed to reduced amounts of gas concentration, temperature, and humidity, even if exposed for prolonged periods.
Other types of physicochemical integrators for ethylene oxide sterilization based on different principles or mechanisms of integration of critical parameters of sterilization could be used if they are also calibrated against a specified validated ethylene oxide sterilization cycle.
The consistency of performance of physicochemical integrators for ethylene oxide sterilization has to be ensured through the testing of performance characteristics at various pre-set selected times for a given ethylene oxide sterilization cycle.
1 Standard for BIER/Steam Vessels, 27 March 1981, Association for the Advancement of Medical Instrumentation (AAMI), 3330 Washington Boulevard, Suite 400, Arlington, VA 22201-4598.
Auxiliary Information Please check for your question in the FAQs before contacting USP.
USP32NF27 Page 718Pharmacopeial Forum: Volume No. 29(1) Page 243