An in vivo but insensate model for the evaluation of antivenoms (ED(50)) using fertile hens' eggs.

The preclinical evaluation of the efficacy of new antivenoms (ED(50)) in animals is required by international regulatory authorities. In vitro testing alone does not provide the end point of lethality of a living system which is essential for an antivenom to prevent. Large numbers of mice are injected with venom/antivenom mixtures and the number of surviving mice is statistically analysed to give an ED(50) value reflecting the efficacy of that antivenom. Our objective was to develop a humane alternative to the conventional rodent ED(50) test using fertile hens' eggs. The egg test combines the advantages of an in vivo system, which gives a clear end point for haemorrhage and lethality, with the certain knowledge that no distress can be experienced by the embryo which is insensate at day 6 of development. Nine different, medically-important venoms and antivenoms were tested by both the rodent and egg ED(50) assays. A good correlation between the two tests was obtained (p<0.01) suggesting that the egg ED(50) method should be considered as an alternative to the rodent ED(50) test for non-neurotoxic venoms. Use of the egg ED(50) test would substantially reduce both the numbers of experimental animals required and also the considerable costs involved in delivering improved clinical treatment of snakebite.