Antibiotics and Painkillers

This lesson covers the difference between antibiotics and painkillers, how antibiotics work, and the critical issue of antibiotic resistance — a key topic in the AQA GCSE Combined Science Trilogy specification (8464).

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Types of Medicine

There are two main categories of medicine you need to know:

Medicine Type	What It Does	Examples
Painkillers	Relieve symptoms of disease (e.g. pain, fever) but do not kill pathogens or cure the disease	Paracetamol, aspirin, ibuprofen
Antibiotics	Kill or inhibit the growth of bacteria inside the body, helping to cure the infection	Penicillin, amoxicillin

Exam Tip: The critical distinction is: painkillers treat symptoms; antibiotics treat the cause (the bacteria). If a question asks "Does this drug cure the disease?", only antibiotics can do this for bacterial infections.

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Painkillers

Feature	Detail
How they work	Block pain signals or reduce inflammation — they make you feel better without affecting the pathogen
Do they kill pathogens?	No — they only relieve symptoms
Can they cure disease?	No — the body's immune system must still fight the infection
When are they useful?	For any illness causing pain or fever, including viral infections where antibiotics cannot be used
Examples	Paracetamol (reduces fever and pain), aspirin (pain relief and anti-inflammatory), ibuprofen (anti-inflammatory)

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Antibiotics

Feature	Detail
How they work	Kill bacteria or prevent them from reproducing inside the body
Do they work against viruses?	No — antibiotics have absolutely no effect on viruses
Why not?	Viruses reproduce inside host cells, using the host cell's own machinery; antibiotics cannot target them without destroying the body's cells
Discovery	Penicillin was discovered by Alexander Fleming in 1928

Why Antibiotics Do Not Work on Viruses

This is one of the most commonly tested concepts:

Feature	Bacteria	Viruses
Cell structure	Prokaryotic cells with cell walls, ribosomes, etc.	Not cells — just genetic material in a protein coat
Reproduction	Binary fission (outside host cells)	Replicate inside host cells
Antibiotic target	Cell wall synthesis, protein synthesis, DNA replication	None — viruses use the host cell's machinery

graph TD
    A[Antibiotic administered] --> B{What type of pathogen?}
    B -->|Bacterium| C[Antibiotic targets bacterial cell wall or ribosomes]
    C --> D[Bacteria killed or prevented from reproducing]
    D --> E[Infection cleared]
    B -->|Virus| F[Virus lives INSIDE host cells]
    F --> G[Antibiotic cannot target virus without destroying host cells]
    G --> H[Antibiotic has NO effect — infection continues]

Exam Tip: If asked "Why can't antibiotics treat viral infections?", say: "Viruses reproduce inside host cells using the host cell's machinery. Antibiotics target bacterial structures (like cell walls) which viruses do not have."

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Antibiotic Resistance

Antibiotic resistance occurs when bacteria evolve to survive treatment with antibiotics. This is one of the biggest threats to global health.

How Does Antibiotic Resistance Develop?

Step	What Happens
1	A population of bacteria contains natural genetic variation — some bacteria may carry a mutation that provides resistance to a particular antibiotic
2	When the antibiotic is used, non-resistant bacteria are killed
3	Resistant bacteria survive and continue to reproduce
4	Resistant bacteria pass on the resistance gene to their offspring
5	Over time, the resistant strain becomes more common
6	The original antibiotic is no longer effective against this population

graph TD
    A[Population of bacteria with genetic variation] --> B[Antibiotic applied]
    B --> C[Non-resistant bacteria killed]
    B --> D[Resistant bacteria survive]
    D --> E[Resistant bacteria reproduce by binary fission]
    E --> F[Resistance gene inherited by offspring]
    F --> G[Resistant strain dominates population]
    G --> H[Antibiotic is no longer effective]

Exam Tip: This is an example of natural selection: variation exists → selection pressure (antibiotic) → survival of the fittest (resistant bacteria) → reproduction and inheritance. Use these key terms in your answers.

MRSA — A Real-World Example

MRSA (Methicillin-Resistant Staphylococcus aureus) is a strain of bacteria that is resistant to several commonly used antibiotics:

Feature	Detail
Full name	Methicillin-Resistant Staphylococcus aureus
Why is it dangerous?	It is resistant to many antibiotics, making it very difficult to treat
Where is it found?	Often in hospitals, where antibiotics are frequently used
Prevention	Strict hygiene in hospitals, screening patients on admission

How Can We Reduce Antibiotic Resistance?

Action	Why It Helps
Only prescribe antibiotics when necessary	Reduces the selection pressure that drives resistance
Complete the full course	Ensures all bacteria are killed, not just the weakest ones
Do not use antibiotics for viral infections	Antibiotics are ineffective against viruses and unnecessary use promotes resistance
Use narrow-spectrum antibiotics	Target specific bacteria rather than killing many different types
Good hygiene in hospitals	Prevents the spread of resistant bacteria between patients
Develop new antibiotics	Provides alternative treatments as old antibiotics become less effective

Exam Tip: You may be asked why doctors should not prescribe antibiotics for viral infections. The answer has two parts: (1) antibiotics are ineffective against viruses, and (2) unnecessary use contributes to antibiotic resistance.

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The Discovery of Penicillin

Feature	Detail
Who	Alexander Fleming
When	1928
How	Fleming noticed that a mould (Penicillium notatum) growing on an agar plate had killed the surrounding bacteria
What happened next	Howard Florey and Ernst Chain later purified and mass-produced penicillin in the 1940s
Significance	Penicillin was the first antibiotic and has saved millions of lives

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Common Mistakes

Mistake	Correction
"Painkillers cure disease"	Painkillers only relieve symptoms — they do not kill pathogens
"Antibiotics work on viruses"	Antibiotics only work on bacteria
"The bacteria become resistant during treatment"	The resistant bacteria already existed due to random mutation before the antibiotic was used — the antibiotic simply selects for them
"Humans become resistant to antibiotics"	It is the bacteria that become resistant, not the human
"We should stop using all antibiotics"	Antibiotics are essential medicines — we should use them responsibly to slow resistance

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Summary