Comparisons between human and animal test data show that most drug side-effects occurring in people cannot be predicted by animal experiments(19). Reliance on animal tests as a guide to safety can therefore be dangerously misleading. For instance, Opren and Eraldin are examples of animal-tested drugs withdrawn from the British market after serious, and in some cases fatal, side-effects in patients(20). The Lancet medical journal acknowledges that "animal tests are very imperfect indicators of human toxicity," and goes on to say that "only clinical experience and careful control of the introduction of new drugs can tell us about their real dangers."(21)
Whilst clinical trials are the most valid test of a new medicine, some preliminary testing using humane alternatives is essential to identify the most toxic substances. In fact hundreds of test tube methods have been developed for the purpose. These include bacteria to test mutagens and carcinogens, yeast to measure phototoxicity, and human tissues to predict skin and eye irritancy. Indeed, tests with human tissue promise better protection since results are directly relevant to people. For instance, chloramphenicol, phenylbutazone, mianserin and thalidomide are examples of medicines whose harmful effects can be identified by human tissue tests but were missed by the original animal experiments(22). As researchers at Britain's Lister Hospital point out, these tests give a degree of reassurance not provided by experiments on animals(23).
Human tissue tests can be supplemented by advanced theoretical techniques which use computer programmes to predict a new drug's toxicity on the basis of it's chemical structure. This approach compares the molecular shape of the test substance with that of drugs and chemicals whose toxic effects are already known(24).
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