B6.4 Developing Drugs

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: preclinical testing, the phases of clinical trials, placebos, double-blind trials and peer review. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Explain why new drugs are tested for toxicity, efficacy and dose
• Describe preclinical testing and the phases of a clinical trial
• Explain the use of placebos and double-blind trials
• Explain why results are peer reviewed before publication
• Interpret and calculate with clinical trial data

Key words

• Toxicity: How harmful a drug is to the body.
• Efficacy: How well a drug works (whether it actually treats the disease).
• Dose: The amount of drug given, and how often.
• Clinical trial: Testing a new drug on human volunteers and patients.
• Placebo: A dummy treatment that looks like the drug but contains no active ingredient.
• Double-blind: Neither the patients nor the doctors know who gets the drug and who gets the placebo.
• Peer review: Other scientists check the work before it is published.

Why drugs must be tested

Every new drug must be tested thoroughly before doctors can prescribe it. Testing checks three things:

• Toxicity – is it safe? Does it harm cells or have serious side effects?
• Efficacy – does it actually work against the disease?
• Dose – what is the best (optimum) amount to give, and how often?

Preclinical testing and clinical trials

Preclinical testing is done in a laboratory: computer modelling, then tests on cells and tissues, then on live animals. Cells show whether the drug harms cells or affects its target, but they cannot show the effect on a whole body, so animals are used next.

• Phase 1; Who takes the drug A small number of healthy volunteers, very low doses at first; What it tests Toxicity and side effects; a safe dose
• Phase 2; Who takes the drug A small number of patients with the disease; What it tests Efficacy (does it work?) and the best dose
• Phase 3; Who takes the drug A large number of patients; What it tests Confirms efficacy and safe doses; finds rarer side effects

Key fact: Very low doses are used first because the drug has never been given to humans; any side effects must be found before many people are exposed.

Placebos and double-blind trials

Patients are split randomly into groups. One group gets the drug and a control group gets a placebo. This shows whether any improvement is really due to the drug, rather than the patient expecting to feel better (the placebo effect).

In a double-blind trial, neither the patients nor the doctors know who has the drug. This stops anyone’s expectations affecting the results – doctors cannot treat the groups differently or record results with bias.

A placebo is not always ethical: it would be wrong to give a dummy pill to a very ill patient. Then the new drug is compared with the best existing treatment.

Peer review and analysing trial data

When a trial is complete, the results are checked by other scientists (peer review) before being published. This helps to stop false claims and checks that the method and conclusions are valid. The drug can then be licensed and sold.

Worked example: using trial data

Effect of the 10 mg dose beyond the placebo = 1.5 − 0.3 = 1.2 mmol per litre.
Going from 10 mg to 20 mg gives only 0.1 more (an increase of 0.1 ÷ 1.5 × 100 = 6.7%).
Higher doses usually bring more side effects, so 10 mg is the best choice.

Answer: optimum dose ≈ 10 mg

Common mistakes

• Saying clinical trials start with patients. They start with healthy volunteers and very low doses.
• Saying a placebo is a “fake drug that cures people”. It contains no active ingredient; it is a control.
• Mixing up blind (patients do not know) and double-blind (patients and doctors do not know).
• Assuming the highest dose is best. The optimum dose works well with the fewest side effects.

Revision questions

Try these, then check your answers below each one.

Question 1. Who receives a new drug first in a clinical trial? (Choose from: A small number of healthy volunteers, at very low doses, A large number of patients, Animals, Doctors.)

Answer: A small number of healthy volunteers, at very low doses

Working: Phase 1 uses healthy volunteers and very low doses to check safety and side effects before patients are involved.

Question 2. In a double-blind trial… (Choose from: neither the patients nor the doctors know who gets the drug, only the patients do not know who gets the drug, the patients are not told they are in a trial, two placebos are used.)

Answer: neither the patients nor the doctors know who gets the drug

Working: In a double-blind trial neither the patients nor the doctors know, so nobody’s expectations can bias the results.

Question 3. True or false? Preclinical testing is carried out on cells, tissues and live animals.

Answer: True

Working: True. Preclinical testing uses computer models, cells, tissues and animals.

Related lessons

• Previous lesson: B6.3 Discovering Drugs
• Next lesson: B7.1 Non-Communicable Diseases
• In this chapter: B6.1 Vaccination
• In this chapter: B6.2 Antibiotics and Painkillers

Continue in the full course

This lesson is section B6.4 (AGCSC0604) of our free GCSE Combined Science course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Combined Science course.