Antibiotics and Painkillers

This lesson covers antibiotics, painkillers and antibiotic resistance as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the difference between antibiotics and painkillers, explain how antibiotic resistance develops (including MRSA), and know the significance of Alexander Fleming's discovery of penicillin.

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What Are Antibiotics?

Antibiotics are medicines that kill bacteria or prevent them from reproducing. They are used to treat bacterial infections.

Key points about antibiotics:

• Antibiotics are specific — different antibiotics work against different types of bacteria.
• Antibiotics work by interfering with bacterial processes such as cell wall synthesis or protein production.
• Antibiotics do NOT work against viruses. This is because viruses reproduce inside host cells using the host's own machinery, so there is nothing for the antibiotic to target without damaging the host cell.

Feature	Antibiotics
Target	Bacteria
Mode of action	Kill bacteria or stop them reproducing
Do they kill viruses?	No
Example	Penicillin
Prescription required?	Yes (in the UK)

Exam Tip: A very common exam question is: "Why can antibiotics not be used to treat viral infections?" The answer is that viruses live and reproduce inside host cells, and antibiotics cannot target the virus without destroying the body's own cells.

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What Are Painkillers?

Painkillers (analgesics) are medicines that relieve pain but do NOT kill pathogens and do NOT treat the cause of disease.

Feature	Painkillers
Target	Pain symptoms
Mode of action	Block pain signals or reduce inflammation
Do they treat the cause?	No — they only relieve symptoms
Example	Paracetamol, aspirin, ibuprofen
Prescription required?	Some (e.g. codeine); many are available over the counter

Comparing Antibiotics and Painkillers

Feature	Antibiotics	Painkillers
What they do	Kill or inhibit bacteria	Relieve pain and symptoms
Treat the cause?	Yes (kill the bacteria)	No (only ease symptoms)
Work against viruses?	No	N/A (they do not target pathogens)
Examples	Penicillin, amoxicillin	Paracetamol, ibuprofen, aspirin

Exam Tip: When treating a bacterial infection, a doctor might prescribe BOTH an antibiotic (to kill the bacteria) AND a painkiller (to relieve symptoms while the antibiotic works). They serve different purposes.

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Alexander Fleming and Penicillin

The discovery of the first antibiotic — penicillin — was one of the most important breakthroughs in medical history.

The Discovery (1928)

1. Alexander Fleming was a bacteriologist studying Staphylococcus bacteria.
2. He left some agar plates uncovered while on holiday.
3. When he returned, he noticed that a mould (Penicillium notatum) had contaminated one of the plates.
4. Around the mould, there was a clear zone where no bacteria were growing.
5. Fleming concluded that the mould was producing a substance that killed the bacteria — he named this substance penicillin.

Development of Penicillin

• Fleming's discovery was initially not widely developed.
• In the 1940s, Howard Florey and Ernst Boris Chain purified penicillin and demonstrated its effectiveness in clinical trials.
• Penicillin was mass-produced during World War II to treat infected wounds, saving millions of lives.
• Fleming, Florey and Chain shared the Nobel Prize in Physiology or Medicine in 1945.

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Antibiotic Resistance

Antibiotic resistance occurs when bacteria evolve to survive exposure to antibiotics that would previously have killed them. This is one of the greatest threats to modern medicine.

How Resistance Develops

Antibiotic resistance develops through natural selection:

1. Within any population of bacteria, there is natural genetic variation — some bacteria may have random mutations that give them resistance to a particular antibiotic.
2. When an antibiotic is used, it kills the non-resistant bacteria.
3. The resistant bacteria survive because the antibiotic does not affect them.
4. The resistant bacteria reproduce, passing the resistance gene to their offspring.
5. Over time, the population becomes dominated by resistant bacteria.
6. The antibiotic is no longer effective against this population.

graph TD
    A["Population of bacteria<br/>some have resistance mutation"] --> B[Antibiotic applied]
    B --> C["Non-resistant bacteria<br/>are killed"]
    B --> D["Resistant bacteria<br/>survive"]
    D --> E["Resistant bacteria<br/>reproduce rapidly"]
    E --> F["New population is<br/>mostly resistant"]
    F --> G["Antibiotic no longer<br/>effective"]

MRSA

MRSA (Methicillin-Resistant Staphylococcus aureus) is a well-known example of an antibiotic-resistant bacterium.

Feature	Detail
Full name	Methicillin-Resistant Staphylococcus aureus
Resistance	Resistant to several commonly used antibiotics, including methicillin
Where it is found	Often in hospitals (a "hospital-acquired infection")
Why it is dangerous	Very difficult to treat because few antibiotics work against it
Prevention	Strict hygiene protocols in hospitals (hand washing, sterilisation of equipment, isolation of infected patients)

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Reducing Antibiotic Resistance

It is essential that we slow the development of antibiotic resistance. Key strategies include:

Strategy	How it helps
Only prescribe antibiotics when necessary	Reduces unnecessary exposure of bacteria to antibiotics; do not use for viral infections
Complete the full course	Ensures all bacteria are killed; stopping early may leave resistant bacteria alive
Do not share antibiotics	Antibiotics are prescribed for specific infections; sharing may lead to misuse
Develop new antibiotics	New drugs can treat resistant strains, but development is slow and expensive
Restrict antibiotic use in agriculture	Overuse in livestock farming accelerates resistance development
Good hygiene in hospitals	Prevents spread of resistant bacteria between patients

Exam Tip: When asked how to reduce antibiotic resistance, three key points are: (1) only prescribe when necessary, (2) patients must complete the full course, and (3) do not use antibiotics for viral infections.

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Summary