Communicable Diseases » Discovering and Developing New Drugs

Where do drugs come from?

A new medicine does not appear overnight. It starts as an idea, then goes through years of discovery, testing and trialling before a doctor is allowed to give it to patients.

Traditionally, drugs were extracted from plants and microorganisms. Three famous examples are on the spec:

• The heart drug digitalis originates from foxgloves.
• The painkiller aspirin originates from willow.
• Penicillin was discovered by Alexander Fleming from the Penicillium mould.

Today, most new drugs are synthesised (made) by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.

Why must new drugs be tested?

New medical drugs have to be tested and trialled before they are used, to check that they are safe and effective. A drug that does not work is a waste of money, and a drug that harms people is worse than no drug at all.

Key terms:

• Toxicity: how harmful a drug is to the body. A toxic drug causes damage.
• Efficacy: how well a drug works, meaning whether it treats the disease.
• Dose: the amount of the drug given. Too little may not work and too much may be harmful.

New drugs are extensively tested for toxicity, efficacy and dose. Every stage of testing is trying to answer these three questions: is it safe, does it work, and how much should be given?

Stage 1: preclinical testing

These tests check the drug for toxicity, efficacy and dose before any person takes it.

Stage 2: clinical trials

If a drug passes preclinical testing, it moves on to clinical trials. These use healthy volunteers and patients.

The trial is done in careful steps:

1. Very low doses of the drug are given at the start of the clinical trial. This keeps people as safe as possible while the first results are collected.
2. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose. This is the dose that works best with the fewest harmful effects.

Placebos and double blind trials

To test efficacy fairly, some patients are given a placebo. A placebo is a substance that looks like the drug but does not contain the drug. Comparing the patients who got the real drug with those who got the placebo shows what the drug itself is doing.

Why not just give everyone the drug? People often feel better simply because they believe they are being treated. The placebo group shows how much of the improvement is down to the drug and how much is down to that belief.

In a double blind trial, neither the patients nor the doctors know who has been given the drug and who has been given the placebo. That stops anyone, even without meaning to, from letting their expectations change what they report or record. The information is only revealed when the trial is over.

Peer review

Doing the trial is not the end. The results of testing and trials are published only after they have been scrutinised by peer review. This means other scientists in the same field check the work first. They look at how the trial was carried out and whether the conclusions are supported by the data.

Peer review helps to make sure that only results that can be trusted are published, so doctors and the public can rely on them.

Putting it together

1. A drug is discovered, from a plant or microorganism, or made by chemists.
2. Preclinical testing: cells, tissues and live animals in a laboratory.
3. Clinical trials: very low doses first, healthy volunteers and patients, then further trials to find the optimum dose.
4. Placebos and double blind trials make the results fair.
5. Results are scrutinised by peer review before they are published.

Exam-style question

A drug company has developed a new drug to lower blood pressure. It is about to start a clinical trial.

(a) Name two things that new drugs are tested for. [2 marks]

(b) Some patients in the trial are given a placebo. Explain why. [2 marks]

(c) The trial is a double blind trial. Describe what this means. [2 marks]