Making medicines

Preclinical development

The promising compounds - often called 'leads' - are then made in small quantities and studied in the laboratory. Initially they will be tested on cell cultures. These are collections of living cells that respond as though they were part of an animal or human. The scientists can determine if the molecules are toxic (poisonous) and if they have any potential therapeutic effects (likely to treat the disease).

At the same time tests will be carried out by chemists and pharmacists to investigate how easily the compounds can be made, how likely they are to be absorbed when given orally (by mouth), and whether there might be other problems with the manufacture of a medicine made from these compounds.

Eventually, after several months of tests, a few molecules will be identified as being the most promising to become an effective medicine to treat the particular disease. These will be tested more rigorously, including tests on animals. These tests will look at whether the medicine is likely to be toxic when given every day for a long time, if it might cause cancer, and if it is likely to cause any damage to the fetus if given to pregnant women.

Before a new compound can be given to humans, tests have to be done to find out:

• whether it is likely to be effective
• whether it is acceptably safe
• whether is is sufficiently stable
• how it is going to be absorbed and excreted by the body