The objective of a combined chronic toxicity/carcinogenicity study is to identify
carcinogenic and the majority of chronic effects, and to determine dose-response relationships
following prolonged and repeated exposure.
The rat is typically used for this study. For rodents, each dose group and concurrent
control group intended for the carcinogenicity phase of the study should contain at
least 50 animals of each sex, while for the chronic toxicity phase of the study should
contain at least 10 animals of each sex. At least three dose levels should be used,
in addition to the concurrent control group for both the chronic toxicity phase and
the carcinogenicity phase of the study. The three main routes of administration are
oral, dermal, and inhalation. The Test Guideline focuses on the oral route of administration.
The period of dosing and duration of the study is normally 12 months for the chronic
phase, and 24 months for the carcinogenicity phase. The study report should include:
measurements (weighing) and regular detailed observations (haematological examination,
urinalysis, clinical chemistry), as well as necropsy procedures and histopathology.
All these observations permit the detection of neoplastic effects and a determination
of carcinogenic potential as well as the general toxicity.