Repeated-Dose, Oral Toxicity 14- and 28-Day Study

In the evaluation of toxic characteristics of any environmental chemical, determination of oral toxicity using repeated doses may be performed after obtaining initial acute toxicity data. This provides information on possible adverse effects that may arise from repeated exposures to the test chemical over a limited period of time. Although there are major similarities in the 28-day and 14-day oral toxicity studies on rodents, the main difference lies in the time over which the dose is administered and the extent of the clinical and pathologic investigations that might be necessary for the shorter period of test. 

Principles of the Test Method Experimental animals will be administered graduated oral doses of the test chemical, daily for a period of 28 or 14 days. Throughout the period of exposure, the animals are observed for clinical signs of poisoning and mortality. Animals that die during the period of test are necrop-sied. The surviving animals are sacrificed and necropsied at the conclusion of the study. 

For the study, a minimum of three dose levels and an appropriate control should be used. Except for the treatment of the test chemical, animals in the control group should be handled in an identical manner to the rest of the groups. The highest-dose level should result in toxic effects in animals but not cause fatalities of a large number of animals, which would interfere with meaningful evaluation of data. Similarly, the lowest dose of the chemical should not produce evidence of toxicity. In contrast, intermediate doses should produce minimal 

It is important to ensure that whenever a chemical is administered in the diet, the quantity used does not interfere with the normal food intake of the animal. Further, when administered in diet, a constant dietary concentration (ppm) or a constant dose level in terms of the test animal s body weight may be used. 

Whenever the chemical is administered by gavage, it should be given at a specific time of the day, and the dose level should be adjusted at a specific interval (e.g., every week or every fortnight). This method maintains a constant dose level in terms of animal body weight. When a repeated-dose study is used as a preliminary to a long-term study, a similar diet should be used. 

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