The questionable value of long-term animal toxicity studies: a regulatory dilemma.

Recommendations for the minimum period of repeated dose administration to animals to support marketing authorization of pharmaceuticals vary from 6 months in the EEC to 18 months in Canada. The value of studies lasting longer than 6 months has not, however, been established. In order to enable retrospective analyses to be carried out, the Centre for Medicines Research has established a toxicology databank containing comprehensive data from repeated dose animal safety evaluation studies on 124 compounds, provided by 21 pharmaceutical companies in Europe (Lumley and Walker 1985a). There are 214 case studies (1 compound tested in 1 species for 1 or more time periods), and in 100 of these tests lasted for longer than 6 months. In 88 long-term studies comparable short-term data are available and these have been analysed to determine what new findings, if any, became apparent after 6 months. The data do not support the need for animal toxicity studies of longer than 6 months, apart from those designed to investigate carcinogenicity. Safety evaluation studies should be of value in predicting adverse drug reactions for man. Unless it can be established that these longer-term studies more accurately define potential target organ effects, the scientific rationale for conventional long-term studies must be questioned.