Animal Testing On Trial

Are animal tests effective?

Animal experiments are conducted in order to increase the researchers’ confidence in a drug, chemical or idea. In this, animal tests are supposed to identify many of the same effects you would see in a human. Depending on the substance tested this might be side effects (safety) and/or positive effects (efficacy). In this way animal tests are supposed to make human trials or human exposure safer and/or more likely to succeed.

The best way of knowing whether animal tests are performing this role is to compare known human effects with the predictions of the animal test, across a number of drugs or chemicals. It is not enough to point to examples where animal tests have been predictive; even a broken watch tells the right time twice a day!

Here is a list of a few studies where this sort of evaluation has been done. The results speak for themselves. Perhaps most shocking is that the results of many animal tests are not even used:

Medical testing

A review of reviews of animal tests and human outcomes found that out of 20 of such 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.)

“Clinicians and the public often consider it axiomatic that animal research has contributed to the treatment of human disease, yet little evidence is available to support this view”. These authors systematically reviewed animal models for six treatments and found that for two human trials were conducted at the same time as the animal studies, while the human trials of three others went ahead despite evidence of harm from the animal studies. “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)

Drug development

Drug development is currently going through a period of crisis. In 2007 the Food and Drug Administration only approved 17 brand new drugs. In their key report on how to improve the development of drugs for people, the Food and Drug Administration 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%.

(Editorial: “Only 17 new molecular entities were approved by the US FDA in 2007, a fall from 53 in 1996”. Science 2008; 320, 1563. 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).

Citation analysis

A review of nearly 100 clinically (human) orientated animal experiments were reviewed for citations by other clinicians. Despite the fact that all the studies were describing treatments and procedures that worked in animals only 8% were cited (noted) by clinical papers and only 4% showed agreement between the animal findings and the human trial.

(Animal experiments in biomedical research. An evaluation of the clinical relevance of approved animal experimental projects. ALTEX 2005; 22(3):143-51.)

HIV

HIV/AIDS vaccines are typically tested on monkeys to see if they are likely to be effective. In the past chimpanzees were used. 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).

Cancer tests

Rodent tests to see if chemicals are likely to be cancerous are notoriously unreliable, as rodents in these situations are more likely to develop cancer. This might be due to species differences or the high levels of stress or doses to which the animals are exposed. In a study reported here, an analysis of more than 500 cancer tests on animals found that although more than 50% were shown to be cancerous in animals, only 34% these were classified as such by the US department responsible. Two other US databases recognise only 15% and 6% of these cancerous chemicals as being cancerous to humans.

(Longer Rodent Bioassay Fails to Address 2-Year Bioassay’s Flaws. Environmental Health Perspectives 2008; 116; A516-7.)

A review of the Environmental Protection Agency’s database of high-risk chemicals found that animal data for 58% of chemicals was considered insufficient to classify human cancer risk, questioning the value of the animal data.

(Which drugs cause cancer? Animal tests yield misleading results. British Medical Journal USA 2005; 5:477-478. And Animal carcinogenicity studies: 1. Poor human predictivity. Alternatives to Laboratory Animals 2006; 34:19-27.)

An analysis of 121 chemicals that were tested twice for carcinogenicity using rats found that different results were obtained in the two tests nearly half the time.

(Data quality in predictive toxicology: reproducibility of rodent carcinogenicity experiments. Environmental Health Perspectives 2001; 109, 509-514)

One study found 19 of 20 substances judged to be safe in humans caused cancer in rodents.

(The predictivity of animal bioassays and short-term genotoxicity tests for carcinogenicity and non-carcinogenicity to humans. Mutagenesis. 1987;2(2):73–78)

Another found that rodent tests identified only 37% of 19 known human carcinogens.

(The lifetime feeding study of mice and rats-an examination of its validity as bioassay for human carcinogens. Fundamental and Applied Toxicology 1983;3:63-67.)

Chimpanzee research

A review of 95 harmful experiments on chimpanzees found that 50% were not referenced (i.e. used in) any other scientific paper and only 14% were referenced in human medical papers. When these papers were reviewed the chimpanzee work was seen to have provided a minimal contribution to knowledge, if at all.

(The Poor Contribution of Chimpanzee Experiments to Biomedical Progress. Journal of Applied Animal Welfare Science, 2008; 10(4), 281–308.)

Stroke research

Over 1,000 potential neuroprotective stroke treatments have been tested in animal models, approximately 100 of these have progressed to human trials, but none have so far proved 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.)

Reproductive toxicity

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.)

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