A scientific review of the progress of animal studies through to human trials and drug development, which showed that one in 20 obtained regulatory drug approval, has led to a debate on the interpretation of the figures.

The 5% figure was based on research, led by Benjamin Ineichen, at the Center for Reproducible Science at the University of Zurich, an EARA member, with a meta-analysis of 122 systematic reviews combining results from over 367 animal studies on therapies for 54 diseases.

While half the therapies tested in animals had results encouraging enough to lead to testing in humans, Dr Ineichen’s analysis, published in PLOS Biology, also found that of those trials whose results were most frequently reproduced in other studies (which indicates how well the research was conducted), 86% led to similar results in humans, indicating that failure to develop new treatments might not lie with the animal studies alone.

While almost all the media coverage of the study focused on the low success rate, Ineichen said: “At first glance, 5% may not seem like a lot. But you have to consider how difficult it is to develop effective new therapies and how great the utility of a drug is for people who suffer from an illness.”

Expert opinions reported by the UK Science Media Centre, also gave their own interpretation of the results.

Lluis Montolliu, at EARA member CNB-CSIC and CIBERER-ISCIII, thought that the 5% figure could come from two sources – that larger human trials are too strict causing some potentially promising animal studies to fail to overcome this barrier, or that there are limitations in the design of both animal experiments and human trials.

He added: “The authors lean towards the second option. And I agree with this interpretation. Animal experiments remain necessary in biomedicine to advance the development of therapies to treat diseases that affect both animals and us, humans. But surely, we should try to improve experimental designs, both at the preclinical and clinical levels, to increase the percentage of animal studies that are confirmed in humans.”

Francisco Javier Cubero, from EARA member Complutense University of Madrid, remarked that clinical trials in humans ‘focus on the response to a therapeutic intervention rather than on the analysis of mechanisms (in animals)’. “Therefore, improving experimental design and incorporating other variables into clinical trials is crucial for improving the success rates of translating experimental therapies to humans.”

Robin Lovell-Badge, at the Francis Crick Institute, UK, noted that there was a significant ‘failure’ rate going from larger human trials to regulatory approval, indicating that a big problem involves developing treatments in humans and need not have much to do with any possible deficiencies in the animal models being used.

To further strengthen the evidence base of animal studies, Ineichen also recommended designing animal experiments to more closely resemble the human trials that may one day follow.

Other issues that mean research using animals is not fully utilised have been highlighted EARA in other Digest articles, including using sample sizes of animals that are too small, not using animals from both sexes to understand their differences and looking more closely at how animal housing  and other environmental factors that affect results.

EARA executive director, Kirk Leech, said: “In the past failure rate figures for the translation of animal studies have hovered around 90%, so no doubt this new 95% figure will be leapt upon by animal groups. What they might also like to consider is the very interesting other suggestions in this report that we should look at how human trials are conducted rather than put the blame solely on the use of animals in research.”

There is, of course, hope that new approaches such as computer simulations and organs-on-chip may one day replace animals, but as an article in The Economist concluded: “Such methods are promising, but have yet to reliably demonstrate whole-body effects in the way that animal models do. For now, at least, animal experimentation is here to stay.”

See also the EARA feature Animal research saves lives. So why do opponents say it is ineffective?