Triggers for Higher Order Toxicity Testing,

Strategies for selecting chemicals for definitive, higher order toxicology tests are important because physical and personnel resources are limited and chemicals vary widely in the need for testing. The National Toxicology Program has developed strategies for selection of chemicals for definitive tests in several are as of toxicology. In addition to the number of people, the extent of human exposure, structure-activity considerations, and reports of observations in humans, specific triggers are sought from animal studies and short-term tests or invitro screening that impact the chemical selection process and the design of definitive studies. Specific triggers in reproductive toxicology, for example, include observations in prechronic toxicology studies in rats and mice weights and histopathologic examinations of reproductive organs, measurements of sperm production and function in males, and estrus cyclicity in females. Comparable tissue-specific triggers do not exist for developmental toxicity studies, and screening tests are not widely used for screening priorities for the conduct of definitive developmental toxicology studies.