DABOURHUB (dabour-hub.com) | 2.6.10 New Medicines | WJEC GCSE Science (Double Award) — Biology

Section 1 of 9Sources of medicines

Many drugs were originally found in plants and microorganisms.

Sources of medicines

Aspirin is based on a chemical from willow bark; digitalis, a heart drug, comes from foxgloves; and penicillin was discovered in a mould by Alexander Fleming in 1928. Today most new drugs are produced by chemical synthesis in laboratories, often after computers or screening identify promising molecules, though natural sources are still searched, especially in rainforests and oceans.

Because new drugs may have powerful effects, they have to be tested to show that they are safe and effective before they can be used.

Section 2 of 9Stages of drug development

1Preclinical testing

Preclinical testing the drug is tested in a laboratory on cells grown in culture and on tissues to see if it works and whether it is toxic.

Then it is tested on live animals, to see how the whole body responds, how the drug is absorbed, distributed and removed,
- and to look for harmful effects.

2Phase 1 clinical trial

Phase 1 clinical trial a small number of healthy volunteers receive increasing doses to check for safety and side effects, and to find a safe dose.

3Phase 2

Phase 2 a larger group of patients with the illness gets the drug to see if it works and which dose is best.

4Phase 3

Phase 3 hundreds or thousands of patients are tested, comparing the new drug with the existing treatment or a placebo.

5Approval and monitoring

Approval and monitoring regulators review the results and, if satisfied, license the drug. Doctors and patients report side effects after release.

The whole process may take 10 years or longer and cost very large sums, which is why new medicines are expensive.

Section 3 of 9Designing a fair trial

A clinical trial must give reliable evidence, so it is designed with care:

Designing a fair trial

Control group

A control group receives either the standard treatment or a placebo, an inactive substance that looks the same as the drug. This allows the effect of the drug to be separated from the psychological effect of believing that one is being treated.

Random allocation

Random allocation of volunteers to groups avoids bias.

Blind

In a blind trial the patient does not know which treatment they have; in a double-blind trial neither the patient nor the doctor assessing them knows, which prevents bias in how results are recorded.

A large sample, similar patients (age, sex, health), and the same dose, timing and conditions for all.

Peer review

Results are checked by other scientists (peer review) before publication, and trials should be repeatable.

Section 4 of 9Evaluating results

To judge a drug, compare the improvement between the two groups.

1

If 70 of 100 patients on the new drug recover compared with 40 of 100 on the placebo, the difference is 30 percentage points, so the drug seems effective.

2

Note the size of the sample, the side effects (for example 12% report nausea) and whether the result could have occurred by chance.

3

Whether a drug is acceptable depends on the balance of its benefits and risks.

4

A drug for a life-threatening illness may be approved with more side effects than a drug for a mild illness.

Section 5 of 9Ethical points

Drug testing raises ethical issues.

1

Animal testing is allowed only when no alternative exists and under strict control, but some people object to it.

2

Volunteers must give informed consent and be told about the risks and are free to withdraw.

3

If a drug works much better in an early trial, it may be unfair to withhold it from the control group.

4

Companies must publish negative results as well as positive ones so that doctors have the full picture.

5

Some medicines are not profitable and so are not developed, for example for rare diseases or those that mainly affect poorer countries.

Section 6 of 9Why trials need large samples and repeats

A drug might seem to work in a small trial simply by chance, because individual people vary in how they respond.

1

A larger sample reduces the effect of chance and of unusual individuals, so the mean result is more reliable.

2

The sample should be representative, with patients of different ages and both sexes, and the groups should be matched.

3

If another research team repeats the trial and obtains similar results, confidence grows; if results differ, the first finding may have been a fluke or due to bias.

4

Regulators also look for side effects that are rare, which show up only when thousands of patients are treated, so monitoring continues after the drug is on the market.

Section 7 of 9Exam-style questions

Explain why a new drug is tested on healthy volunteers in the first human trials. [2]2 marks
Describe what is meant by a double-blind trial and why it is used. [3]3 marks
In a trial, 80 of 200 patients taking a new drug improved and 50 of 200 taking a placebo improved. Calculate the percentage in each group who improved and suggest a conclusion. [3]3 marks

Section 8 of 9Key terms

Term	Meaning
Placebo	An inactive treatment that looks like the real drug.
Double-blind trial	A trial where neither patient nor doctor knows who has the drug.
Clinical trial	Testing of a drug on human volunteers.
Preclinical testing	Laboratory and animal testing before human trials.
Control group	A group not given the treatment being tested.
Peer review	Evaluation of scientific work by other experts.
Informed consent	Agreement given after being told the risks and benefits.
Side effect	An unwanted effect of a drug.

Section 9 of 9Exam technique

1

Saying that a placebo contains the drug. It is an inactive substance.

2

Forgetting that double-blind means the doctors are unaware too.

3

Believing that animal testing alone proves a drug is safe for humans.

4

Concluding a drug works without comparing with a control group.

5

Ignoring sample size when evaluating a trial.