Chronic toxicity is a property of a substance that has toxic effects on a living organism, when that organism is exposed to the substance continuously or repeatedly. Compare to acute toxicity.
Initial acute toxicity studies are conducted to determine the lethal dose (LD or LD --the dose required to kill 50% or 90%, respectively, of the laboratory animals), toxic symptoms, and the time symptoms appear.
Chronictoxicity studies, conducted in at least two species (including one nonrodent), usually last the lifetime of the animal (up to 2 yr in a rodent or longer in a nonrodent), but duration may depend on the intended duration of drug administration to humans.
These tests and chronictoxicity studies may be conducted concurrently with initial studies in humans, particularly when the drug is intended only for short-term human use.
Chronictoxicity is the adverse effects occurring as a result of the repeated daily exposure of experimental animals to a chemical by the oral, dermal, or inhalation routes of exposure.
Cumulative toxicity is the adverse effects of repeated doses occurring as a result of prolonged action on, or increased concentration of, the administered test substance or its metabolites in susceptible tissue.
The findings of a chronictoxicity study should be evaluated in conjunction with the findings of preceding studies and considered in terms of the toxic effects as well as the necropsy and histopathological findings.
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