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6.4 Developing Drugs

GCSE Biology · AQA · Chapter 6: Preventing and Treating Disease

A free GCSE Biology lesson for AQA (8461) from OBA School: preclinical testing, 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 stages 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 drug.
  • 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, first on cells and tissues, then on live animals. Testing on cells shows whether the drug harms cells or kills a pathogen, but cells cannot show the effect on a whole body, so animals are used next.

Clinical trials use people. First, very low doses are given to small numbers of healthy volunteers to check that the drug is safe. If it is, trials move on to patients with the disease, using different doses to find the optimum dose and to measure efficacy.

Key fact: Low doses are used first because the drug has never been given to humans and 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 – the doctors cannot treat groups differently or record results with bias.

Placebos are 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.

Worked example: using trial data

Effect of the drug at 20 mg beyond the placebo = 15 − 4 = 11 mmHg.
Going from 20 mg to 40 mg gives only 1 mmHg more (an increase of 1 ÷ 15 × 100 = 6.7%).
Higher doses usually bring more side effects, so 20 mg is the best choice.

Answer: optimum dose ≈ 20 mg

Common mistakes

  • Saying clinical trials start with patients. They start with healthy volunteers and low doses.
  • Saying a placebo is a “fake drug that cures people”. It contains no active drug; 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 the drug first in a clinical trial? (Choose from: Healthy volunteers, at very low doses, Patients, at high doses, Animals, at very low doses, Doctors.)

Answer: Healthy volunteers, at very low doses

Working: Very low doses are given to healthy volunteers first to check the drug is safe in humans.

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 blindfolded, the drug is tested on two groups of animals.)

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 expectations cannot 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 is done in the lab on cells, tissues and live animals.

Related lessons

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This lesson is section 6.4 (AGCBH0604) of our free GCSE Biology 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 Biology course.

 

 

 

 

 

 

 

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