Tests alternative to the rabbit bioassay for pyrogens

The rabbit bioassay is currently the only legally acceptable method to test for pyrogenic contamination of parenteral preparations and medical devices designed to enter the parenterum. However, research efforts have recently made available alternative procedures to test for pyrogens which may have significant value in quality control. Part of the reluctance to accept tests other than the rabbit test may be due to the low visibility of emerging understanding of a significant theory of testing in which it is contended that the parameters of sensitivity and specificity are inversely related and that accuracy is an ideal. The rabbit pyrogen assay will detect 1 to 10 ng of enterobacteriaceal endotoxin (ET). The limulus test will detect 0.01 to 0.1 ng/ml of ET; some of the other tests approach the rabbit assay in sensitivity. Since it is current dogma that pyrogen is equivalent to ET, the basis for the use of ET to standardize pyrogen tests is rationalized. The source of ET in practice is bacterial contamination; therefore, numbers of bacteria that contaminate parenteral preparations can be directly related to potential pyrogenicity. Further, viable counts of bacteria in parenteral preparations, prior to sterilization, is a reliable test for pyrogens. Other tests such as nitroblue tetrazolium reduction and actinomycin-D enhancement of lethality of pyrogen for mice deserve consideration in quality control procedures. The limulus test, the most practical of currently available alternative tests for detection of ET and therefore, of pyrogen has application where the rabbit test cannot be used. Therefore, control personnel must learn of the availability, performance and interpretation of the limulus test. Practical considerations must govern the choice of an alternative test when the use of a test other than the rabbit bioassay is indicated.