Filters challenge testing

Used to validate and monitor radiation sterilization processes Vaccine against whooping cough 0.22-pm filter challenge test... 

Verification of the microbial retention efficiency of the membrane filters may be undertaken using either Hquid or aerosol challenge tests. A Hquid challenge test is more stringent. Furthermore, this test can provide retention information for process conditions such as extreme moisture after sterilization or air entrained with water drops. A Hquid challenge is performed using a protocol similar to that described for Hquid filtration. 

HEPA filter evaluation (airborne particulate levels, smoke-challenge testing, velocity measurements, etc.)... 

The search for the ideal nondestructive test of a sterilizing fdter system is still proceeding. One new suggestion has been proposed to use test gas pressures above the bubble point. In the meantime, the wise user of filter systems for sterilization will test in as many ways as possible and correlate for physical tests with bacterial challenge tests. 

Filter media are not repetitive-use items, and although used for more than one lot in production, the media are usually discarded after some predetermined number of uses or time. Therefore, it is impossible to test every filter medium individually, since the challenge test is a destructive test. The nondestructive tests, therefore, require a high degree of correlation with a retention test. When such correlated tests are established and controls maintained, filtration users can depend on filtration to produce a sterile parenteral product. 

Figure 13 Hypothetical disk-filter bacterial challenge test appartus.

The challenge test results are then observed. The challenge tests are considered invalid if the negative control contains any organisms. The filter system is considered to have failed the test if the filtrate contains any test organisms. 

The test should have been correlated with a bacterial challenge test (BDT). The FDA considers a sterilizing grade filter as one that produces a sterile filtrate when challenged with 10 Pseudomonas diminuta per cm2 of filter surface. 

Before performing a product bacteria challenge test, it has to be assured that the liquid product does not have any detrimental, bactericidal or bacteriostatic, effects on the challenge organisms. This is done utilizing viability tests. The organism is inoculated into the product to be filtered at a certain bioburden level. At specified times, the log value of this bioburden is tested. If the bioburden is reduced due to the fluid properties, a different bacteria challenge test mode becomes applicable. ... 

Fevy, R.V. The effect of pH, viscosity, and additives on the bacterial retention of membrane filters challenged with pseudomonas diminuta. In Fluid Filtration Liquid American Society for Testing and Materials (ASTM) Washington, DC, 1987 Vol. II. 

Gas niters may be evaluated prior to use by the same methods used for liquid filters (see Section 111 below), allowing that they can be effectively dried out and sterilized without loss of the qualities being tested. Alternatively they may be evaluated by exposure to particles in a gas stream, for instance by the sodium name test, which is also used for HEPA filters. Microbiological tests have to be considered in a somewhat different light. Leahy and Gabler 71 describe an aerosol challenge test of 10 Ps. diminuta bacteria per mL over a four-day period as an appropriate manufacturer s validation test. It would not be practical for routine use. 

The process used for sterilization by dry heat should include air circulation within the chamber and the maintenance of a positive pressure to prevent the entry of non-steriie air. If air is supplied, it should be passed through a microorganism-retaining filter. Where this process of sterilization by dry heat is also intended to remove pyrogens, challenge tests using endotoxins would be required as part of the validation. 

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