Communicable Diseases (AQA GCSE Biology): Revision Notes
New medicines
All new medicines must go through careful testing before doctors can use them. This makes sure they are safe and work properly to treat diseases.
What are medical drugs?
A medical drug is any substance that treats the cause of a disease or helps reduce its symptoms. These drugs help people get better when they are ill.
Medical drugs work by either targeting the root cause of a disease or by helping to manage the symptoms that patients experience, making them feel better and helping their bodies recover.
Where do drugs come from?
Traditional plant sources
For hundreds of years, people discovered medicines by using plants and natural substances. Many important drugs still come from these traditional sources today.
Examples of traditional medicines:
- Digitalis - comes from foxglove plants and treats irregular heartbeat
- Aspirin - comes from willow bark and leaves, used for aches and pains
- Penicillin - comes from Penicillium mould and fights bacterial diseases
Historical Discovery: Penicillin
Alexander Fleming discovered penicillin in 1928 when he noticed that mould had killed bacteria in one of his laboratory dishes. This accidental discovery became one of our most important antibiotics, saving millions of lives by fighting bacterial infections.
Modern synthetic drugs
Most new drugs today are synthesised. This means scientists make them using chemical reactions in laboratories. The pharmaceutical industry employs many scientists who work to create these new medicines.
Synthetic drugs allow scientists to create medicines with very specific properties and effects, often improving on natural compounds or creating entirely new treatments that don't exist in nature.
How are new drugs tested?
New drugs must be tested extensively to check three important things:
- Toxicity - how poisonous or harmful they might be
- Efficacy - how well they work at treating a disease
- Dose - how much drug is needed for it to work properly
Stage 1: Preclinical testing
Before testing on people, new drugs are tested in laboratories using:
- Cell cultures - growing cells in dishes to test the drug
- Tissue cultures - testing on small pieces of body tissue
- Live animals - testing on laboratory animals like mice
Preclinical testing helps scientists identify promising drugs and eliminate potentially dangerous ones before any human testing begins. This stage can take several years to complete thoroughly.
This helps scientists find promising drugs that might work safely.
Stage 2: Clinical trials
Once a drug passes laboratory tests, it moves to testing on people:
Clinical Trial Process
Phase 1: Very small doses are given to healthy volunteers to check the drug is not toxic to people.
Phase 2: If the drug is found to be safe, different doses are given to patients who have the disease. This helps find the optimum dose - the amount that works best.
Double blind trials
Scientists use special methods to make drug testing fair and accurate.
In a double blind trial:
- Some patients get the real drug
- Some patients get a placebo (fake medicine that looks identical)
- Neither the doctors nor the patients know who gets what
This stops the placebo effect from affecting results. The placebo effect happens when people feel better just because they think they are taking medicine, even when it's not real medicine.
Double blind trials give the most reliable results because they prevent bias from affecting the outcomes. Without this method, results could be influenced by what patients and doctors expect to happen rather than what the drug actually does.
Remember!
Key Points to Remember:
- All new medicines must be tested for safety and effectiveness before use
- Traditional medicines come from plants and natural sources like digitalis and aspirin
- Modern drugs are mostly synthesised in laboratories
- Drug testing has two stages: preclinical (lab testing) and clinical trials (people testing)
- Scientists test for toxicity, efficacy and the right dose
- Double blind trials using placebos give the most reliable results