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4.2.8Topic 4 · Biodiversity and Natural Resources

Development of Drug Testing — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

5 min read 8 parts Lesson 19 of 22 1 quiz

📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision
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4.2.8 Development of Drug Testing — Edexcel A Level Biology A (SNAB) 9BI0 notes: Describe how new drugs are developed and tested, including the roles of placebos, blinding, trials and ethics.Many medicines originate from plants, for example aspirin from willow bark and digoxin fr…

  • Discovery and screening
  • Pre-clinical testing
  • Phase 1 clinical trial
  • Licensing and phase 4
  • Double-blind
  • Randomisation

Section 1 of 8Why testing is needed

Many medicines originate from plants, for example aspirin from willow bark and digoxin from foxglove.

Why testing is needed
A new drug must be shown to be safe, effective and of good quality before it is licensed.
Testing has become much more rigorous since the thalidomide disaster of the late 1950s and early 1960s, when a drug given to pregnant women for morning sickness had not been tested in pregnancy and caused severe limb malformations in thousands of babies.

Section 2 of 8Stages of development

1Discovery and screening
Discovery and screening potential compounds are identified from plants, microbes or chemical libraries, and tested on cultured cells for biological activity.
2Pre-clinical testing
Pre-clinical testing tests on cells, computer models and animals examine toxicity, how the drug is absorbed, distributed and removed, and the effective dose.
3Phase 1 clinical trial
Phase 1 clinical trial small group of healthy volunteers tests safety, side effects and dose.
4Phase 2
Phase 2 a few hundred patients with the condition, testing efficacy and optimum dose.
5Phase 3
Phase 3 large randomised controlled trial with thousands of patients comparing the new drug with the best existing treatment or a placebo.
6Licensing and phase 4
Licensing and phase 4 regulators review the evidence; after approval, monitoring of long-term side effects continues in the general population.

Section 3 of 8Reducing bias

To obtain valid data, clinical trials are designed to remove bias:

Placebo
Placebo an inactive substance that looks identical to the drug. Comparing patients receiving the drug with those receiving placebo shows how much improvement is due to the drug and not the expectation of being treated (the placebo effect).
Double-blind
Double-blind neither patients nor doctors know who receives which treatment until the data are analysed, so expectations cannot influence reporting or assessment.
Randomisation
Randomisation patients are assigned to groups by chance, so groups are similar in age, sex and health.
Large sample size
Large sample size and matched groups increase reliability, and results are published in peer-reviewed journals so others can scrutinise them.

A placebo is not used when withholding treatment would be unethical, for example in life-threatening disease; then the new drug is compared with the existing treatment.

Section 4 of 8Ethical issues

Ethical concerns include the welfare of animals used in pre-clinical tests (the principles of replacement, reduction and refinement), informed consent of volunteers, the risk of harm in early trials, fairness in selecting patients, confidentiality, and the cost of medicines.

Ethical issues
Some argue plants and the habitats which provide new compounds should be conserved, and local communities who hold traditional knowledge of medicinal plants should share in any profits (the idea of benefit-sharing).
Trials should be stopped early if the drug shows serious harm or is clearly beneficial.

Section 5 of 8Statistics, ethics and plant-derived drugs

Data from trials are analysed to decide whether any difference between drug and placebo is real or could be due to chance.

Statistics, ethics and plant-derived drugs
Statistically significant
A result is described as statistically significant when the probability of obtaining it by chance is less than 5 percent (p less than 0.05).
A larger sample and a well-controlled design increase confidence.
Side effects
Researchers also report side effects, and regulators weigh the benefits against the risks: a drug for a deadly cancer may be approved despite unpleasant side effects, whereas one for a mild headache may not.

Plants have been a rich source of drugs: the anti-cancer compound paclitaxel from the Pacific yew, the heart drug digoxin from foxglove, and the antimalarial artemisinin from sweet wormwood.

1
Collecting from the wild can threaten species, so many compounds are now made by cultivation or synthesis.
2
Because there are species not yet studied, losing biodiversity could mean losing future medicines.
3
This provides an economic argument for conservation.
4
When you evaluate trial evidence in an exam, comment on sample size, controls, blinding, duration, whether the study is peer reviewed, who funded it and whether the results can be repeated by others.

Remember also that preclinical and clinical stages take many years and cost hundreds of millions of pounds, and most candidate compounds fail at some stage.

Statistics, ethics and plant-derived drugs
This is one reason medicines can be expensive and why companies seek patents.
Some compounds are tested in vitro on cultured human cells first, which reduces animal use, and computer models are increasingly used to predict how a molecule will bind to a target protein before any laboratory synthesis is attempted.

Section 6 of 8Exam-style questions

  1. Explain why a double-blind trial with a placebo is used when testing a new drug. [4]4 marks

  2. Suggest why drugs are tested on healthy volunteers in Phase 1. [2]2 marks

  3. In a trial, 120 of 400 patients on a new drug recovered compared with 60 of 400 on placebo. Calculate the percentage point difference in recovery and comment. [3]3 marks

Section 7 of 8Key terms

TermMeaning
PlaceboInactive substance resembling the drug used for comparison.
Double-blind trialTrial in which neither patients nor researchers know who gets which treatment.
RandomisationAllocating subjects to groups by chance.
Clinical trialTest of a drug on human volunteers or patients.
Pre-clinical testingLaboratory and animal tests before human trials.
ThalidomideDrug that caused birth defects because it was not adequately tested.
Informed consentVolunteer agrees after being told all risks and benefits.
Peer reviewScrutiny of research by independent experts before publication.

Section 8 of 8Exam technique

1
Saying a placebo is a weak drug: it is an inactive substance.
2
Confusing single-blind (patient unaware) with double-blind (patient and researcher unaware).
3
Suggesting Phase 1 involves patients with the disease: it normally uses healthy volunteers.
4
Stating that animal testing alone proves drugs are safe in humans.
5
Ignoring informed consent when discussing ethics.

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