An evaluation of some proposals for a reduction in the number of animals used for the potency testing of diphtheria and tetanus vaccines.

Analysis of data from small subgroups of animals used in potency tests for vaccines containing diphtheria and tetanus components has shown that, in most cases, satisfactory assurance of potency can be obtained with much smaller numbers of animals than are currently prescribed by the pharmacopoeias. It is suggested that when the criterion of potency for a vaccine is defined in terms of the lower fiducial limit of potency, the additional prescription of a minimum number of animals for the test is unnecessary. Furthermore, when well standardized, lyophilized toxins are used for challenge, there is no need to determine the LD50 of the challenge toxin on every occasion. The possibility of obtaining assurance of potency with smaller numbers of animals using single point comparisons of unknown and standard vaccines is also discussed.