4.3.1.9 - Discovery and Development of Drugs

Where drugs come from

A drug is a chemical that affects processes in the body. In this specification point, the word is being used for potential new medical medicines, not for illegal drugs.

Traditionally, useful drugs were extracted from plants and microorganisms. AQA names three examples:

These examples are memory facts, but they also show the wider idea: living organisms can contain chemicals that affect human biology.

Most new drugs are now synthesised by chemists in the pharmaceutical industry. Synthesised means made by chemical reactions rather than simply collected from an organism. However, the starting point may still be a useful chemical first extracted from a plant.

What testing checks

New medical drugs have to be tested and trialled before they are used. The main reason is to check that they are safe and effective.

Testing for toxicity checks whether the drug could harm the body. In exam answers, "to check toxicity", "to check it is safe" and "to check for harmful side effects" are the same idea, so do not list them as separate points if the question asks for different reasons.

Testing for efficacy checks whether the drug actually treats the disease or symptom it is meant to treat. This is different from efficiency. Efficacy is the AQA word for whether it works.

Testing for dose finds out how much of the drug should be given. The aim is to find a dose that is high enough to be effective but not so high that the risk of harm is unacceptable. The best dose for treatment is called the optimum dose.

Preclinical testing

Preclinical testing happens before clinical trials in humans. It is done in a laboratory using cells, tissues and live animals.

Cells and tissues can show whether a drug affects living material in the intended way and whether it damages cells. Live-animal testing can give more information about effects in a whole organism. At GCSE, the key point is not the detailed method; it is that preclinical testing is laboratory testing before human clinical trials.

[DIAGRAM: asset_name: drug-development-pipeline - diagram 1; asset_slug: 038_4_3_1_9_discovery_and_development_of_drugs_diagram1; file: diagram_assets/imagegen_regen_all/038_4_3_1_9_discovery_and_development_of_drugs_diagram1_imagegen.png; recommended_method: codex_image_gen; description: Monochrome flowchart showing drug discovery from traditional extracts or synthesised compounds, preclinical testing on cells, tissues and live animals, clinical trials with healthy volunteers and patients, double blind placebo comparison, and peer review before publication.]

Preclinical results help scientists decide whether it is reasonable to move to human trials. A drug that looks promising in the laboratory still has to be trialled in people, because cells, tissues and animals cannot prove exactly how the drug will behave in humans.

Clinical trials

Clinical trials are drug trials in humans. AQA states that clinical trials use healthy volunteers and patients.

Clinical trials begin cautiously. Very low doses of the drug are given at the start of the clinical trial. This reduces the risk to volunteers and patients while scientists look for evidence about safety.