The necessary minimal duration of final long-term toxicologic tests of drugs.

The optimal, and thus mandatory duration of final, long-term toxicologic tests of drugs in animals prior to marketing for use in human beings remains controversial. Some regulatory authorities contend that exposure for 6 or 12 months is adequate. However, the Bureau of Human Prescription Drugs of the Health Protection Branch of Health and Welfare Canada has evaluated a number of confidential reports from manufacturers in which significant, non-neoplastic, pathologic changes occurred only after exposure of animals for more than 1 year. Fifteen examples from these files and the literature are described. These studies support the current Canadian guidelines' requirement for the duration of final long-term toxicologic tests of drugs to be at least 18 months.