Human epidemiological studies have the power to save millions of lives, showing that major advances can be achieved without animal experiments. Although prevention is obviously better than cure and deserves the greatest emphasis, not all disease can be avoided. Again, non-animal methods make an important contribution to the cure of disease and are increasingly replacing animals. For instance, analysis of British figures shows that between 1977 and 1995, the use of living animals to develop and test drugs fell by around 60%, reflecting the increased use of more humane techniques. In fact, almost any useful drug effect can be identified in the test tube using cells, tissues and enzymes from the body.(14) The AIDS treatment AZT originated from in vitro experiments (15) (as did the drug combinations now being used against HIV), whilst anti-cancer agents can be assessed in the test tube using human cancer cells. Based on the idea that medicines must be the right shape to trigger their effects on the tissues, scientists are employing 3D computer graphics to design new treatments. At present however, in vitro methods are usually seen as preliminary tests prior to experiments on animals.
Discovering whether a potential new drug has useful effects is only the first step in development. The next stage is to assess its safety prior to clinical trials with healthy volunteers and patients. Although animals are overwhelmingly used for the purpose, they are not the only way and hundreds of in vitro tests have been developed. 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 have the advantage over animal experiments that results are directly relevant to people. Although the method has not hitherto been widely used there are sufficient examples to show that it could improve safety:
*Human bone marrow cells can identify drugs such as chloramphenicol and phenyIbutazone which cause potentially fatal aplastic anaemia, (16) a side effect not predicted by the original animal tests.
*Human liver tissue can detect hepatic toxicity associated with the anti-epileptic drug valproic acid (17) although extensive animal experiments prior to marketing failed to identify the problem.
*Thalidomide's effect on the foetus can be studied with human embryonic tissue (18) although many animal species proved resistant to the drug.
Theoretical techniques to predict toxicity are also emerging. Unilever has developed a computer method called DEREK which can identify potential skin sensitisers on the basis of chemical structure. DEREK compares the new chemical with substances whose sensitisation is already known. Unilever use DEREK as the first stage in identifying suspect chemicals: test on animals usually follow.(19)
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