Antibiotics and painkillers — AQA GCSE Combined Science
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Antibiotics and painkillers explained
Antibiotics are medicines that treat bacterial infections by killing infective bacteria or stopping their growth inside the body.
Read the full explanation
They are ineffective against viruses, so treating influenza or the common cold with penicillin wastes medicine and can encourage resistance. Other medicines treat disease in different ways: painkillers such as paracetamol relieve symptoms but do not kill pathogens, while antivirals slow viral replication and vaccines prevent disease rather than cure it. For example, a patient with a chest infection caused by Streptococcus bacteria may be prescribed amoxicillin, whereas a patient with a viral sore throat needs rest, fluids and symptom relief. Understanding the target of each medicine lets you explain why a treatment is chosen and why finishing a prescribed course matters.
Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics.
Antibiotics such as penicillin cure bacterial disease by killing infective bacteria inside the body. Penicillin interferes with bacterial cell wall formation, so the bacteria burst and die, while human cells are unaffected because they lack a cell wall. Because bacterial species differ in structure and metabolism, a medicine that works on one species may not work on another; for example, penicillin is effective against many Streptococcus infections but not against Mycobacterium tuberculosis. Doctors therefore identify the pathogen, often by laboratory culture or a rapid test, before prescribing. Using the wrong antibiotic wastes time, allows the infection to worsen and increases the chance of resistant bacteria surviving and multiplying.
The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. However, the emergence of strains resistant to antibiotics is of great concern.
Antibiotics are medicines that kill bacteria or stop them growing, so they treat infectious bacterial diseases such as tuberculosis and bacterial meningitis. Their widespread use since the mid-20th century has greatly reduced deaths from these diseases. However, bacteria reproduce rapidly and mutations can produce strains that are not affected by an antibiotic. When antibiotics are used, susceptible bacteria die but resistant bacteria survive and reproduce, so the resistant strain spreads. Overuse and incomplete courses increase this selection pressure. This is of great concern because infections caused by resistant strains, such as MRSA, are harder to treat and may become untreatable.
Antibiotics cannot kill viral pathogens.
Antibiotics work by interfering with structures or processes found in bacteria, such as bacterial cell walls or bacterial protein synthesis. Viruses are not cells; they are much smaller and reproduce only inside host cells. They have no bacterial cell wall and no bacterial metabolism for an antibiotic to target, so antibiotics cannot kill viral pathogens. This is why antibiotics do not cure viral infections such as influenza, the common cold or measles. Viral infections may be treated with antivirals, and vaccination can prevent them. Painkillers relieve symptoms but do not kill pathogens. Understanding this difference helps explain why antibiotics should not be prescribed for viral illnesses.
Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens.
Painkillers such as paracetamol relieve symptoms like headache, fever or pain, but they do not destroy the pathogen causing the infection. They act on the body's pain and temperature pathways rather than on bacteria or viruses, so the immune system must still clear the pathogen. Other medicines may also treat symptoms without killing pathogens; for example, oral rehydration solutions replace water and ions lost through diarrhoea, and antihistamines reduce allergic symptoms. This contrasts with antibiotics, which kill bacteria or stop their growth. A patient with a bacterial throat infection may take a painkiller to reduce soreness while an antibiotic kills the bacteria. Understanding this distinction prevents the misconception that any medicine that makes you feel better is fighting the infection itself.
It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
Viruses reproduce inside host cells, so a drug that kills the virus must either enter the host cell or interfere with viral replication without harming the host cell. Because viruses use the host cell's machinery, many antiviral targets are also present in human cells, making it hard to avoid damage to body tissues. This is why antibiotics do not work on viruses and why developing antiviral drugs is challenging. For example, a drug that blocks viral protein synthesis might also block human protein synthesis, causing side effects. Antiviral drugs therefore tend to target virus-specific enzymes or structures, but even then side effects can occur. The immune system usually clears viruses, and vaccines help prevent viral infections.
Your focus
- State that antibiotics kill infective bacteria and are ineffective against viruses.
- Distinguish between medicines that cure infection and medicines that only relieve symptoms.
- Justify a treatment choice by linking the type of pathogen to the action of the medicine.
Show all 18 objectives
- Describe how antibiotics such as penicillin kill infective bacteria inside the body.
- Explain why a specific antibiotic is needed for a specific bacterium.
- Apply knowledge of antibiotic specificity to a named infection scenario.
- State that antibiotics kill bacteria and have greatly reduced deaths from bacterial diseases.
- Explain how mutation and selection lead to antibiotic-resistant strains.
- Describe why resistant strains are of great concern and how overuse contributes.
- State that antibiotics cannot kill viral pathogens.
- Explain why antibiotics are ineffective against viruses by comparing bacterial and viral structure.
- Identify viral infections that are not treated with antibiotics.
- State that painkillers treat symptoms of disease but do not kill pathogens.
- Distinguish between medicines that relieve symptoms and antibiotics that kill bacteria.
- Explain why a patient may still need their immune system to clear an infection when taking a painkiller.
- Explain why it is difficult to develop drugs that kill viruses without damaging body tissues.
- State that antibiotics do not work on viruses.
- Describe how viruses reproduce inside host cells and why this complicates drug development.
Antibiotics and painkillers exam tips
Marking Points
- Antibiotics kill infective bacteria inside the body or prevent their growth, so they cure bacterial disease rather than merely masking symptoms.
- Antibiotics do not kill viruses, so they cannot cure viral diseases such as influenza, measles or the common cold.
- Painkillers such as paracetamol or aspirin relieve pain and lower fever but do not destroy pathogens, so the immune system still has to clear the infection.
- Other medicines act differently: antivirals slow viral replication, and vaccines stimulate immunity to prevent disease rather than treat an existing infection.
- Choosing the correct medicine depends on identifying the type of pathogen, because a bacterial infection and a viral infection need different treatments.
- Completing a prescribed course of antibiotics reduces the chance that surviving bacteria multiply and spread, including resistant strains.
- Antibiotics are medicines that cure bacterial disease by killing infective bacteria inside the body.
- Penicillin is an example of an antibiotic and works by disrupting bacterial cell wall formation, causing the bacteria to burst.
- Antibiotics are selective: a specific antibiotic is effective against particular bacteria, not against all bacteria.
- Identifying the pathogen, for example by laboratory culture or a rapid test, allows the correct antibiotic to be prescribed.
- Using an ineffective antibiotic allows the infection to continue and can allow resistant bacteria to survive and multiply.
- Antibiotics do not work on viruses, so they should not be prescribed for viral infections.
- Antibiotics kill bacteria or inhibit their growth, so they treat bacterial infections such as tuberculosis.
- Antibiotic use has greatly reduced deaths from infectious bacterial diseases.
- Random mutation can produce bacteria that are resistant to an antibiotic.
- When an antibiotic is used, susceptible bacteria die while resistant bacteria survive and reproduce, so the resistant strain increases in frequency.
- The emergence of resistant strains is of great concern because infections become harder or impossible to treat.
- Overuse of antibiotics and not completing a prescribed course increase the chance of resistance developing.
- Antibiotics kill bacteria by targeting bacterial structures or processes.
- Viruses are not cells and lack the bacterial targets that antibiotics act on.
- Therefore antibiotics cannot kill viral pathogens.
- Viral infections such as influenza or the common cold are not cured by antibiotics.
- Antivirals and vaccines, not antibiotics, are used against viral pathogens.
- Painkillers relieve symptoms such as pain, fever or inflammation but do not kill pathogens.
- Painkillers act on the body's symptoms rather than on the pathogen itself.
- Other medicines, such as oral rehydration solutions, treat symptoms or replace lost substances without killing pathogens.
- Antibiotics are different because they kill bacteria or inhibit bacterial growth.
- The immune system still has to destroy the pathogen when only symptom-relieving medicines are used.
- A named example, such as paracetamol for a headache, can illustrate symptom relief without pathogen destruction.
- Viruses reproduce inside host cells, so drugs must affect the virus without harming the host cell.
- Many antiviral targets are similar to human cell processes, so damage to body tissues is a risk.
- Antibiotics do not kill viruses, which is why viral infections are not treated with antibiotics.
- Antiviral drugs are difficult to develop because they must be selective for virus-specific features.
- The immune system and vaccines are important in defence against viral infections.
- A named example, such as a drug that blocks a viral enzyme, can show how selectivity is attempted.
Examiner Tips
- 💡Name the pathogen type first, then name a suitable medicine and state its action, for example 'bacterial infection, so penicillin kills the bacteria'.
- 💡Use the phrase 'relieves symptoms' for painkillers and 'kills bacteria' for antibiotics so the distinction is explicit.
- 💡When asked to explain, link the medicine to the disease and to the reason it works, rather than listing medicine names alone.
- 💡Link the antibiotic to its mechanism, for example 'penicillin prevents cell wall formation so bacteria burst', to show understanding rather than recall.
- 💡When explaining specificity, give a named example such as penicillin for a Streptococcus infection and state why it would not treat a viral infection.
- 💡Use the term 'specific' explicitly when describing how the correct antibiotic is chosen for a particular bacterium.
- 💡Use the phrase 'resistant strain' rather than saying a person is resistant.
- 💡Link each point to natural selection: mutation, survival, reproduction and spread.
- 💡Give a named example such as MRSA to show the concern is real.
- 💡Contrast bacteria and viruses in one sentence to show why antibiotics fail against viruses.
- 💡Name a viral infection to support your answer.
- 💡Mention that antivirals or vaccines are used for viral infections.
- 💡State clearly that painkillers treat symptoms and do not kill pathogens, using the word 'symptom' explicitly.
- 💡Contrast painkillers with antibiotics in one sentence to show the difference in action.
- 💡Use a named example such as paracetamol or ibuprofen to support the explanation.
- 💡Explain that viruses reproduce inside host cells and link this to the difficulty of selective drug action.
- 💡State that antibiotics are ineffective against viruses to contrast with the challenge of antiviral drug development.
- 💡Use the phrase 'without damaging the body's tissues' to address the second clause of the statement.
Common Mistakes
- Error: stating that antibiotics cure viral diseases such as influenza. Correction: antibiotics act on bacteria, so viral infections need antivirals, rest and symptom relief instead.
- Error: claiming painkillers kill the bacteria causing an infection. Correction: painkillers only relieve symptoms such as pain and fever; they do not destroy pathogens.
- Error: saying all medicines are antibiotics. Correction: antibiotics are one class of medicine; antivirals, painkillers and vaccines work by different mechanisms.
- Error: saying one antibiotic treats every bacterial infection. Correction: different antibiotics target different bacteria, so the pathogen must be identified first.
- Error: claiming penicillin kills viruses as well as bacteria. Correction: penicillin acts on bacterial cell walls, which viruses do not have.
- Error: describing antibiotics as painkillers. Correction: antibiotics kill bacteria, whereas painkillers only relieve symptoms such as pain or fever.
- Saying antibiotics kill viruses: correct this by stating that antibiotics act on bacteria, not viruses.
- Thinking resistance develops because the body becomes used to the antibiotic: correct this by explaining that bacteria mutate and resistant strains are selected.
- Believing a person can become resistant rather than the bacterial population: correct this by saying the bacterial strain becomes resistant.
- Claiming antibiotics can treat flu or the common cold: correct this by stating that these are viral and antibiotics do not kill viruses.
- Confusing painkillers with antibiotics: correct this by saying painkillers relieve symptoms but do not kill pathogens.
- Thinking antibiotics work against all pathogens: correct this by specifying that they act on bacteria only.
- Thinking that painkillers kill the pathogen because the patient feels better; correction: painkillers only relieve symptoms, and the immune system or another medicine must remove the pathogen.
- Confusing painkillers with antibiotics; correction: antibiotics target bacteria, whereas painkillers do not kill bacteria or viruses.
- Assuming all medicines are antibiotics; correction: medicines include symptom relievers such as painkillers and rehydration solutions as well as antibiotics.
- Thinking antibiotics can treat viral infections; correction: antibiotics kill bacteria, not viruses, and do not work on viral diseases such as colds or flu.
- Assuming antiviral drugs are harmless because they target viruses; correction: they can still damage body tissues because viruses use host cell processes.
- Believing viruses are easily killed outside cells; correction: viruses replicate inside host cells, so drugs must act within the body without harming host cells.