Surprisingly, most scientists do not regularly review the predictability of animal tests as part of their work- there is an assumption that animal tests work based on certain similarities with humans and long history of use. But it is not enough to come up with one or two examples of where animal tests appear to have been helpful. Just because animals were used as part of the drug discovery process also does not mean that they had to be used, nor that they were a key part. To be an effective scientific approach, animal testing needs to be consistently predictive – but this is far from the case.
“The claim that animal experimentation is essential to medical development is not supported by proper, scientific evidence but by opinion and anecdote. Systematic reviews of its effectiveness don’t support the claims made on its behalf.” (Pound, P. et al. 2004. British Medical Journal 328, 514-7.)
Where reviews of the predictability and utility of animal tests have been done, the results have been damning:
A review (of reviews) of animal tests and human outcomes found that out of 20 reviews, only two concluded that the animal tests were consistent with the human findings or had contributed significantly to developing new treatments.
(Systematic Reviews of Animal Experiments Demonstrate Poor Human Clinical and Toxicological Utility. ATLA 2007; 35, 641–659.)
A review of 76 important animal tests for human therapeutic drugs found that, despite all the animal studies showing that the drug in question worked safely, only 55% were then repeated in human trials and of these, one third were found to produce conflicting results to what had been reported in the animal studies, i.e. treatments were not actually effective. The authors concluded that “patients and physicians should remain cautious about extrapolating the findings of prominent animal research to the care of human disease”.
(Translation of research evidence from animals to humans. Journal of the American Medical Association 2006; 296, 1731-2.)
A review of ‘animal models’ for six treatments found that for two of the treatments human trials were conducted at the same time as the animal studies, while for another three human trials went ahead despite evidence of harm from the animal studies. The authors concluded; “This suggests that the animal data were regarded as irrelevant, calling into question why the studies were done in the first place and seriously undermining the principle that animal experiments are necessary to inform clinical medicine”.
(Where is the evidence that animal research benefits humans? British Medical Journal 2004; 328:514-7.)
A follow up review of a further six interventions for various human diseases found that the ‘animal models’ failed to accurately predict the human outcome in four cases. For two of these the animal tests actually suggested the drug would be helpful when it was in fact harmful.
(Comparison of treatment effects between animal experiments and clinical trials: systematic review. British Medical Journal 2007; 334; 197-200)
In its key report on how to improve the development of drugs for people, the Food and Drug Administration (FDA) noted that the chances of a drug being suitable for human patients even after it had passed all the animal and other laboratory studies, was only 8%.
(Innovation or stagnation: Challenge and opportunity on the critical path to new medicinal products. US Department of Health and Human Services, Food and Drug Administration; March 2004).
A review of the predictability of animal tests to predict acute toxicity conducted by the drug industry found that out of 150 drugs, tests on rats and mice only predicted 43% of human effects.
(Concordance of the toxicity of pharmaceuticals in humans and in animals. Regulatory Toxicology and Pharmacology 2000; 32: 56-67).
A recent review of the animal and human trials of HIV vaccines found that: “To date, 85 candidate AIDS vaccines have been tested in 197 clinical trials, comprising several main types…Just 12% of these trials have reached Phase II, only seven
(3.5%) have reached Phase III, and altogether, 18 trials were prematurely terminated. None has been successful."
(An Assessment of the Role of Chimpanzees in AIDS Vaccine Research. Alternatives to Laboratory Animals 2008; 36, 1–48).
A review of over 1,000 potential neuroprotective stroke treatments that had been successfully tested in animal models, found that only approximately 100 progressed to human trials, but none were successful. Of these approximately 50% were tested in humans before the animal tests were published.
(1,026 Experimental Treatments in Acute Stroke. Annals of Neurology 2006; 59, 467-77.) A review of tests to find out whether chemicals affect the development of unborn animals found that the animal tests only predicted damage to human foetuses just over 50% of the time – in other words, virtually no better than tossing a coin.
(The future of teratology research is in vitro. Biogenic Amines 2005; 19:97–145.)