This law holds that everything is teratogenic if given in the right dose to the right species at the right time. It follows that because all agents have the potential for toxicity in some organism at some dose, the production of positive results in developmental toxicity studies is only a matter of finding a sensitive state in a sensitive species and of using an adequately high dose of the toxicant. The choice of rats and rabbits as the primary testing species is not because they are considered to be so similar to humans, but because they are easy to handle and because their use has generated an enormous, although not necessarily correct, database.
Different species develop at different rates and along different schedules.
These differences can affect the interpretation of animal data because chemicals appear to exert their effect on the fetus at different stages of development. Humans may be more sensitive than other animals because of the longer period of human development. Species-specific differences in the placenta may affect the results of animal tests. The route of administration to the animal may not be the likely human route. It is not unusual to see drugs given to animals in teratogenicity tests intraperitoneally, intravenously, or via gastric tubes.