A critical appraisal of the duration of chronic animal toxicity studies

One method of assessing the contribution of studies of longer than 6 months to a safety evaluation program is to compare retrospectively the findings in toxicity tests carried out for 6 months or less with those observed after 6 months. The Centre for Medicines Research has therefore established a databank comprising animal toxicological data obtained from pharmaceutical companies in Europe. Twenty-one companies have provided data for 124 compounds (214 studies), including 88 studies of 65 compounds where comparable short-term (⩽6 months) and long-term (>6 months) data are available. The results from the 88 studies show that, excluding the possibility of identifying carcinogens, tests of longer than 6 months have not added to the overall safety evaluation of these compounds.