During the development of a new medicine, the compound must be tested to see if it is likely to have any harmful effects on patients.

Compounds that have the potential to become medicines are assessed for toxicity and a safety profile is created for each. As medicines are designed to be active in the body, researchers tread a fine line trying to make the drug as effective as possible whilst minimising any harmful side effects.

The toxicity assessment for each potential medicine is carried out in single cells or cell cultures in vitro and in whole animals in vivo. During the development of a new medicine the compound is also tested to see if it is likely to have any harmful effects on patients. The combination of in vitro, in vivo and human studies provides the safety and effectiveness profile of the compound required by the regulatory authorities for registration of a new medicine.

In vivo toxicology

There is a legal requirement for animal tests to be carried out on all potential medicines. Alternative, non-animal methods are used  where validated tests are available; however currently these methods are limited in number as in vitro tests  may not necessarily correspond with how a compound will behave in a living animal.

All work involving animals is strictly regulated through the Animals (Scientific Procedures) Act in the UK. The law ensures that the animal houses, laboratories and animal care procedures meet very high standards and that animal use is kept to the minimum that will achieve the regulatory requirements. There are also inspections held regularly both in-house and un-announced by independent government inspectors.

Every research project has to be approved before it can start and the likely benefits are considered against any possible distress caused to the animals. Scientists who carry out experiments involving animals also have to hold a Personal License which is only given to people who have the necessary education and training to perform that type of experiment.

The role of the toxicologist

The principle role of the toxicologist is to be able to understand and evaluate the results of the animal studies and relate them to possible adverse effects in man. Interpretation of the findings from animal studies is imperative to determine what may occur in the human population. Some of the effects seen may be due to the pharmacological effects of the compound when high doses are given or may be due to the way it is broken down (metabolised) by the animal.

Tests must be carried out to assess the effects of repeated doses looking for changes in the blood or urine or other abnormal signs. At the end of the study the animals will be killed and  organs examined for changes at the cellular level that may be due to the compound. The effects of the medicine in reproductive function and on the offspring of animals dosed while pregnant also needs to be established.

Any changes which may represent a potential hazard to man must be carefully investigated and considered so that the potential benefit of the new medicine can be balanced against the possible risks.

People who work in toxicology

For those who wish to follow a career in the field of toxicology, toxicology modules can be studied as part of several degree courses such as medicinal chemistry, biochemistry, pharmacology or pharmacy. Once you have obtained a relevant degree , there are a number of post graduate courses in which toxicology is taught as a single subject or combined with a second subject such as forensic science.

Last modified: 20 October 2023

Last reviewed: 20 October 2023