A drug safety test that uses thousands of laboratory mice and rats each year in Europe is no longer necessary, a review involving 18 pharmaceutical companies and contract research organisations has found.

Published in the journal Regulatory Toxicology and Pharmacology, the review co-ordinated by the UK-based National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3RS) concluded that information gained from the single-dose acute toxicity test, usually conducted in rodents before an investigational compound moves into clinical trials, has little or no value in assessing a drug’s potential risk to humans.

Acute toxicity is defined as toxicity produced after administration of a single dose of a compound in a period not exceeding 24 hours and up to a limit of 2,000mg/kg (or the maximum dose technically achievable). The main rationale for the test is to identify drugs with potential to cause major adverse effects and/or life-threatening toxicity. As the NC3RS/industry review points out, this often involves estimating the minimum lethal dose in rodents.

As a result, the regulatory requirement for acute toxicity testing of any pharmaceutical intended for human use has proved particularly contentious. In the drug development sphere, it is the only study type to carry lethality/life-threatening toxicity as an endpoint as documented in current regulatory guidelines. The scientific value of the data obtained and their usefulness in predicting acute toxic effects in humans have also been a matter of dispute, especially in view of the effects on the animals used.

In the meantime, the review notes, a change in pharmaceutical industry strategy over recent years has meant that early toxicology data are now frequently used to sift out the most promising compounds for further evaluation. “Acute toxicity tests are often no longer the first toxicology studies conducted, therefore prompting this re-assessment of acute toxicity tests in pharmaceutical drug development,” the authors state.

The review led by AstraZeneca’s Dr Sally Robinson (Robinson, S. et al., A European pharmaceutical company initiative challenging the regulatory requirement for acute toxicity studies in pharmaceutical drug development, Regul. Toxicol. Pharmacol. (2008), doi:10.1016/j.yrtph.2007.11.009) examined preclinical and clinical data on 74 compounds contributed by members of a European industry working group set up in 2003 to consider the need for acute toxicity testing. Of these compounds, 34 were dropped before administration to humans and 40 proceeded to clinical trials.

The researchers concluded that acute toxicity data were:

- Extremely limited with respect to the parameters assessed in the review, which focused on minimum lethal and maximum non-lethal doses.
- Less useful than other, less harmful animal tests, which were better for determining appropriate doses to be administered in further animal studies.
- Did not provide information on the nature of toxic effects, which were better evaluated in other routine studies.
- Were not, in practice, used to set doses in first human clinical trials as other routine studies provided more informative data.

“The results show that there should be no requirement for stand-alone acute toxicity studies as these are not pivotal in human safety assessment,” the authors said.

Next steps
The next step will be to persuade regulatory bodies worldwide that acute toxicity testing prior to clinical trials should no longer be a requirement of drug development. The working group is also looking at whether these studies are necessary at a later stage of development (e.g., Phase III trials or at registration) to predict potential drug effects in overdose.

As the review points out, the “only possible clinical reason for conducting acute toxicity studies is to support risk assessment in humans at a time when patients will have uncontrolled access to large quantities of drug, although the usefulness of the limited animal dataset provided is still questionable”. An ongoing collaboration with the Lyon Poison Centre will be pivotal in determining whether acute toxicity data are needed to assist in overdose management, the authors note.

In global regulatory terms, there is a window of opportunity in the International Conference on Harmonisation’s current revision of its guidelines on the timing of preclinical studies in relation to clinical trials (ICH M3). As the paper in Regulatory Toxicology and Pharmacology points out, the latest draft of the revised ICH guidance incorporates in full the recommendations made by the European industry working group on the basis of the 40 compounds that entered clinical trials.

There were:

- Acute toxicity studies should not be required prior to the first clinical trial in humans.
- Any short term or dose-escalation data (including from non-GLP [good laboratory practice] studies) should be considered acceptable to allow assessment of acute toxicity, and this should be by the clinical route only.
- In situations where overdosing may be a cause for concern (e.g., where there may be uncontrolled access to the drug, as in Phase III clinical trials or at registration), establish, by reviewing both the pre-clinical and clinical dataset, whether additional high dose information is necessary. In the majority of cases a stand-alone acute toxicity study should not be required.
- Lethality should not be the primary endpoint.
- Rather than using a second rodent species, data should be provided from a rodent and a non-rodent species, preferably from short duration studies that are already an integral part of drug development and that include parameters in the study design that assist risk assessment.

Marked impact
As the NC3RS observes, it may be 18 months to two years yet before the revised ICH M3 guidelines come into force. However, the working group review has already had a marked impact on individual company policies, with a reduction of over 70% in animal use for acute toxicity tests by the 18 companies involved. According to the NC3RS, none of these efforts have encountered resistance from regulatory bodies to date.

Toxicity testing of new medicines for humans and animals accounts for 4% of all animal use across Europe, with just under half a million mice and rats subjected to these tests each year. The review of acute toxicity testing is expected to cut that figure by around 15,000 rodents per year in Europe, equating to about 3.5% of the mice and rats used to test new human and veterinary medicines or dentistry products. “While we recognise that this reduction represents a small proportion of the total, it is an important step in the right direction,” Dr Robinson commented.

Dr Kathryn Chapman, who co-ordinated the project for the NC3RS, said the approach used “shows that significant progress can be made by going back to first principles and examining the need for a particular test, rather than trying to replace the test with non-animal methods. It also highlights that impressive results can be achieved when companies share appropriate data in a focused way, and the NC3RS has adopted a similar approach in other areas of animal use.”

The companies involved in the European initiative include AstraZeneca, Roche, Eli Lilly, Johnson & Johnson, Pfizer, Novartis, Sanofi-Aventis, GlaxoSmithKline, Charles River Laboratories, Covance and Huntingdon Life Sciences. The project is supported by the European Federation of Pharmaceutical Industries and Associations (EFPIA).