Robert Koch: Human research isolated the cholera microbe when it proved impossible to reproduce the disease in laboratory animals
Despite such evidence, medical science came to rely on animal models of human disease perhaps because animals are regarded as disposable species whereas investigation of human patients requires so much more skill and patience in avoiding unnecessary risks. Nevertheless it is acknowledged that animal models are generally poor and in some cases non-existent (5) which explains why many treatments that work on animals fail when given to humans. It also explains why so many useful drug effects are only identified during clinical studies of human patients.
In view of the widespread use of animals to develop and test new medicines, it is surprising that there have been so few attempts to see how well they predict effects in people. An indication of the accuracy of animal tests can be obtained by the failure rate of drugs during clinical trials. For instance, studies reported in the 1960s showed that 97.7% of new drug candidates selected for clinical trial failed to reach the market.(6) Similar findings were reported by Ciba Geigy in 1965 when 95% of chemical compounds found safe and effective on the basis of animal tests were discarded during clinical trials.(7) A more recent analysis in the United States once again revealed that the majority of new medicines (68% in this case) subjected to clinical trials never reached the market.(8) The survey was carried out between 1963 and 1976 and listed the main reasons for discarding the drugs as lack of efficacy in treating patients, human toxicity and inappropriate action of drugs within the human body (pharmacokinetics).
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