BioEd Online

Just how useful are animal experiments in predicting the outcome of human trials of new medicines?

Animal-rights activists have long claimed that differences between humans and animals make experiments in species such as rats of little use. Most scientists disagree, saying that drug development would be impossible without initial tests in animals (see our Animal research special).

Now a team of medical researchers has published in the BMJ¹ results from what they say is the first attempt to produce a scientific, quantitative answer to this question. The results provide food for thought for any scientist who works with animals.

The authors say they have highlighted serious problems with the way in which animal research is translated into human trials. Only half of the small sample of tests analysed by the team so far produced the same results in animals as they did in people.

The team stresses that this is not an argument against doing animal studies. Even so, the paper is likely to be seized on by activists.

Data match

The researchers started by taking six sets of clinical trials that had produced definitive answers as to whether specific treatments for conditions such as stroke and head injury are useful or not. They then assessed whether the prior animal research had given similar results to the human trials. The results, published today, say that the sets of data matched in only three of the six cases.

When the team investigated the reasons for this, they exposed a series of problems with the animal data. Many studies did not allocate animals randomly to control and treatment groups, a problem that is known to introduce bias into clinical trials. Comparison of experiments on a stroke treatment also suggested that studies showing negative effects are more likely to go unpublished, skewing impressions of efficacy.

Work on a model of head injury was undermined by the use of a model that did not match the later clinical trials. Rodents were injured and then treated five minutes later, says Ian Roberts, an author on the study and an epidemiologist at the London School of Hygiene and Tropical Medicine. In the clinical trials, which are based on hospital admissions, patients are typically treated within three hours of being injured.

Design challenge

Although the results could be seen as evidence that animal work does little to inform clinical studies, the authors stress that their results show only that more time needs to spent thinking about how to translate research between the two spheres. Better-designed models and an awareness of publication bias are two priorities, they say.

Other researchers question whether the results are really as alarming as they sound. Robert Lechler, an immunologist at Kings College London, says that designers of clinical trials are already well aware of limitations in animal models. He says that scientists apply an "intelligent filter" when looking at such tests, and that crude comparisons between the outcomes of animal and human studies do not capture this.

But Peter Sandercock, a neurologist at the University of Edinburgh and an author on the study, says the paper shows that more needs to be done on this front. If such a filter was applied, he points out, the animal models of head injury would have been repeated using a better design before human studies started. "This is not a polemic against animal research," stresses Sandercock. "But we need to be aware that there are biases in the animal trials."

Visit our newsblog to read and post comments about this story.