Drug Development and Testing

This lesson covers drug development and clinical testing as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the stages of drug testing (preclinical and clinical trials), the use of placebos and double-blind techniques, and why rigorous testing is necessary.

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Why Do New Drugs Need Testing?

Before any new medicine can be given to patients, it must be thoroughly tested to ensure it is:

1. Safe — it does not cause harmful side effects (or that any side effects are acceptable compared to the benefits)
2. Effective — it actually works to treat or prevent the disease
3. Stable — it can be stored and used without breaking down
4. Able to be absorbed — it can reach the target site in the body

Without rigorous testing, dangerous or ineffective drugs could reach patients, causing harm or giving false hope.

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Where Do New Drugs Come From?

New drugs can be discovered from a variety of sources:

Source	Example
Plants	Aspirin was originally derived from willow bark; digitalis (a heart drug) comes from foxgloves
Microorganisms	Penicillin was discovered from the mould Penicillium notatum
Chemical synthesis	Many modern drugs are designed and synthesised in laboratories
Computational methods	Computer modelling can predict which molecules may be effective

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Stages of Drug Development and Testing

Drug development follows a series of rigorous stages:

graph TD
    A["1. Discovery and<br/>target identification"] --> B["2. Preclinical testing<br/>Lab and animal studies"]
    B --> C["3. Phase I clinical trial<br/>Small group, safety"]
    C --> D["4. Phase II clinical trial<br/>Larger group, effectiveness"]
    D --> E["5. Phase III clinical trial<br/>Large-scale, comparison"]
    E --> F["6. Regulatory review<br/>and approval"]
    F --> G["7. Phase IV<br/>Post-market surveillance"]

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Stage 1: Discovery and Target Identification

• Scientists identify a disease target (e.g. a specific protein or pathway involved in the disease).
• Thousands of candidate molecules are screened to find those that interact with the target.
• The most promising candidates are selected for further testing.

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Stage 2: Preclinical Testing

Preclinical testing takes place in the laboratory before any testing on humans.

Testing on Cells (In Vitro)

• Candidate drugs are tested on human cells or tissues grown in the laboratory.
• This checks whether the drug has any effect on the target cells and whether it is toxic to healthy cells.
• "In vitro" means "in glass" — referring to laboratory glassware.

Testing on Animals (In Vivo)

• Drugs that pass cell testing are then tested on live animals.
• This tests the drug in a whole, living organism to check:
  • Efficacy — does it work in a living body?
  • Toxicity — is it harmful to organs or systems?
  • Dosage — what is a safe and effective dose?
• Animal testing is legally required in the UK before clinical trials on humans can begin.
• "In vivo" means "in the living" — referring to tests in living organisms.

Testing type	What it means	Purpose
In vitro	Testing on cells / tissues in the lab	Initial safety and effectiveness checks
In vivo	Testing on living organisms (animals)	Check effects in a whole organism; determine dosage

Exam Tip: Animal testing is a controversial topic, but for the exam you need to know that it is legally required before human trials. It allows scientists to check for unexpected harmful effects in a living organism.

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Stage 3: Clinical Trials (Testing on Humans)

If preclinical tests are successful, the drug progresses to clinical trials on human volunteers.

Phase I — Safety

Feature	Detail
Participants	Small number of healthy volunteers (typically 20–100)
Purpose	Test safety; identify side effects; determine safe dosage range
Key question	Is the drug safe for humans?

Phase II — Efficacy

Feature	Detail
Participants	Larger group of patients who have the disease (typically 100–500)
Purpose	Test whether the drug actually works (is effective); continue monitoring side effects
Key question	Does the drug treat the disease?

Phase III — Large-scale Comparison

Feature	Detail
Participants	Very large group of patients (typically 1,000–5,000+)
Purpose	Compare the drug with existing treatments or a placebo; confirm effectiveness across a diverse population
Key question	Is the drug better than current treatments?

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Placebos

A placebo is a fake treatment that looks identical to the real drug but contains no active ingredient (e.g. a sugar pill or saline injection).

Why Use Placebos?

• To ensure that any improvement in patients is genuinely due to the drug and not due to the placebo effect — a psychological phenomenon where patients feel better simply because they believe they are receiving treatment.
• Comparing results from the drug group with the placebo group shows whether the drug has a real therapeutic effect.

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Double-Blind Trials

In a double-blind trial:

• Neither the patient nor the doctor knows who is receiving the real drug and who is receiving the placebo.
• This prevents bias — doctors might unconsciously treat patients differently if they know who has the drug, and patients might report different symptoms depending on whether they think they are receiving the real treatment.

Trial type	Who knows?	Purpose
Open	Both patient and doctor know	Quick testing; less reliable
Single-blind	Patient does not know; doctor does	Reduces patient bias
Double-blind	Neither patient nor doctor knows	Eliminates both patient and doctor bias

Exam Tip: The double-blind method is the gold standard for clinical trials. When asked why it is used, always mention that it prevents bias from both the patient and the doctor, making results more reliable.

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Stage 4: Regulatory Review

• Once Phase III trials are complete, all data is submitted to a regulatory body for review.
• In the UK, this is the MHRA (Medicines and Healthcare products Regulatory Agency).
• The regulatory body reviews the evidence for safety, efficacy and quality.
• If approved, the drug is licensed for use by doctors and patients.

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Stage 5: Post-market Surveillance (Phase IV)

• Even after a drug is approved, its effects continue to be monitored.
• Rare side effects that were not detected in clinical trials may emerge when the drug is used by millions of people.
• If serious problems are found, the drug can be withdrawn from the market.

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Summary of the Drug Testing Pipeline