Why successful animal trials do not always guarantee human safety
In short: Testing new treatments in animals can reveal potential pitfalls, yet the transition to human clinical trials remains incredibly complex. While animal models have historically been pivotal for ensuring safety, the results often fail to translate directly to human biology, leaving regulators to navigate a difficult scientific gap.
The journey from laboratory discovery to a licensed medicine is a decade-long process. There is often a time lag of more than 10 years between the initial animal studies used to support early clinical testing and the moment a company submits a Marketing Authorisation application. Because of this significant delay, regulatory bodies like the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) will likely continue to review applications containing animal study results for the foreseeable future.
Current international guidelines, such as those from the ICH, provide specific frameworks for these studies. For example, the ICH M3 R2 recommendations suggest that if a clinical trial is intended to last at least 6 months, it should be supported by 6-month general toxicity studies in rodents and 9-month studies in non-rodents. Furthermore, the World Health Organization still indicates that animal immunisation studies should be conducted during vaccine development.
However, the landscape is shifting. The MHRA is committed to the 3Rs principles—replacing, reducing, or refining animal use—and the UK government policy aims to phase out animal testing. While alternative, non-animal methods are advancing, regulators acknowledge they currently share similar limitations with animal studies in predicting human effects. The MHRA remains open to proposals that omit animal studies if the developer can scientifically justify that alternative methods sufficiently address safety risks.
This transition creates a period where two different approaches may coexist: one developer might use traditional animal models, while another uses only non-animal-based methods. The regulator's priority remains the safety of patients, evaluating each application individually to ensure that any deviation from international norms does not pose a risk to human health.
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Sources
- Summary by Intellect · source: How We Go from Animal Model to Clinical Trial
- Also: MHRA approach to medicines using non-animal methods
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