Nevertheless, in toxicity tests, progress in completely replacing animals is frustratingly slow. All too often in vitro systems are seen as a preliminary means of assessment, to be carried out prior to final confirmation in animals. In the case of the Draize test, in vitro methods are used to identify and eliminate the most severe irritants. Although this can reduce animal suffering, and the number of rabbits used, it means that chemicals not thought to be severely irritating, go on for final assessment in animals. This is reflected in the British statistics: after falling substantially through the 1980s, the number of rabbits remained fairly constant thereafter. In 1995, 4,037 were used, just 179 less than in 1990.(39)
Many non-animal tests have been devised to identify human cancer-causing chemicals, and they too are seen as 'pre-screens'. Here, they are used to alert toxicologists to hazardous substances which are then subjected to animal experiments. The result is that the use of animals for carcinogenicity testing has only slowly declined.
The perception is that test-tube techniques must be superior to their animal counterparts before finally being accepted. Clearly it is necessary to make sure that any new test predicts human responses with reasonable accuracy but in vitro tests are subjected to far greater scrutiny than animal experiments have ever been! The process is known as 'validation': a number of chemicals whose effects are already known, are assessed using the new technique. Some scientists have suggested a 'pre-validation' stage to ensure that the validation process itself is properly planned. In fact, a scientific workshop on the subject identified five main stages - test development, pre-validation, validation, independent assessment, and progression towards acceptance by official government bodies.(41) Actually devising a non-animal test seems a minor problem compared to getting it accepted.
The irony is that animal safety tests have never been properly validated (21) and even the briefest study shows only a 5-25% correlation between human and animal test results.(42) It should therefore be common sense that any new in vitro test is assessed using human data. Unfortunately most validation studies utilise previous animal research findings. Using vivisection as a basis to assess new methods imbues animal experiments with a validity they do not deserve. Furthermore, any lack of concordance between animal and in vitro results will reflect poorly on the alternative technique, yet it could be accurately predicting how people react.
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