Studies with the International Pyrogen Standard on the sensitivity and reproducibility of pharmacopoeial pyrogen testing.

Rabbits, 27 or 36 in each experiment, were injected with the International Pyrogen Standard (I.P.St.) in different seasons. The maximum temperature rises were registered, randomized and interpreted according to the requirements of the B.P. (1973), U.S.P. (1970), P. Hung. (1970) and P. Nord. (1962). Although the dose of 3.5 ng kg(-1) I.P.St. proved to be non-pyrogenic as tested in summer, when tested in winter the same dose was qualified pyrogenic (to be rejected) by up to one third of the combinations by the criteria of the four Pharmacopoeias. In the spring experiment "to be rejected" qualifications predominated as based on the response of large groups of rabbits. Exclusion of the rabbits showing low sensitivity (before randomization) barely influenced the results with 3.5 ng kg(-1) I.P.St. in the experiment in which the mean temperature rise was 0.49 degrees. If, however, the mean temperature rise was higher (0.57 or 0.69 degrees), such a selection practically resulted in the disappearance of "passable" qualifications in the triplet groups and a great predominance of "to be rejected" qualifications in the larger groups. The dose 7.0 ng kg(-1) consistently proved to be pyrogenic in large groups of rabbits.