🔬 The right match
A doctor works out which bacteria are causing the illness, then chooses the antibiotic that kills those bacteria.
Communicable Diseases » Antibiotics and Painkillers
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.3.1.8
- How antibiotics such as penicillin cure bacterial disease
- Why antibiotics do not work on viruses, and why antiviral drugs are hard to make
- How painkillers and other medicines treat symptoms but do not kill pathogens
- Why resistant strains of bacteria are a great concern
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Unlock This CourseMedicines that cure: antibiotics
Your body can often fight off an infection by itself, using the defences and white blood cells you have already met. Sometimes it needs help. Medicines are drugs that are used to treat disease, and different medicines do very different jobs.
The most famous medicines for infections are antibiotics. Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing the infective bacteria inside the body. Once the bacteria are dead, they can no longer reproduce or release toxins, so the disease clears up.
Key terms:
- Penicillin: an antibiotic that kills bacteria inside the body.
- Painkiller: a medicine that treats the symptom of pain. It does not kill pathogens.
- Symptom: a sign of disease that you can feel, such as pain, a high temperature or a cough.
- Resistant strain: a type of bacteria that antibiotics can no longer kill.
Using the right antibiotic
There are many different kinds of bacteria, and they are not all the same. An antibiotic that kills one kind may do very little to another. This means it is important that specific bacteria should be treated by specific antibiotics.
❌ The wrong match
An antibiotic that does not kill the bacteria causing the illness will not cure it, so the patient stays ill.
What antibiotics have achieved
The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. Illnesses that once killed many people can now often be cured with a short course of tablets or an injection.
However, there is a problem. Bacteria can change, and strains that are resistant to antibiotics have emerged. A resistant strain is not killed by the antibiotic, so the disease can no longer be treated in the usual way. The emergence of resistant strains is of great concern, because bacterial infections could become much harder to treat. How resistant strains arise, and how we can slow them down, is covered in the lesson on Extinction and Resistant Bacteria.
Antibiotics cannot kill viruses
Antibiotics cannot kill viral pathogens. They only work on bacteria. So an antibiotic is no use at all against a cold, flu or measles, because these are caused by viruses.
Why is it hard to make drugs that kill viruses?
Viruses reproduce inside your own body cells. A drug that gets in to kill the virus is very likely to damage your body's tissues as well. This is why it is difficult to develop drugs that kill viruses without also damaging the body's tissues. Bacteria are different: they are separate living cells, so a drug can attack them without harming you in the same way.
Because of this, the best protection against many viral diseases is not a cure but prevention, such as the vaccination you studied in the previous lesson.
Medicines that treat symptoms: painkillers
Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens. For example, paracetamol and ibuprofen can ease a headache or lower a high temperature when you have an infection. You may feel better, but the pathogens are still in your body until your immune system clears them or a suitable medicine kills them.
| Medicine | What it does | Kills the pathogen? |
|---|---|---|
| Antibiotic such as penicillin | Cures bacterial disease | Yes, bacteria only |
| Painkiller | Treats symptoms such as pain | No |
Worked example
A student has a cough and a high temperature. A doctor tests and finds the cause is a virus. Should the doctor prescribe an antibiotic?
No. Antibiotics cannot kill viral pathogens, so it would not cure the illness. The student can take a painkiller to treat the symptoms while the immune system fights the virus.
Common mistakes
Saying that antibiotics kill all pathogens. They only kill bacteria. Another mistake is to say that painkillers cure disease. They treat symptoms such as pain, but they do not kill the pathogen.
Putting it together: which medicine?
In an exam you may be given a situation and asked which medicine, if any, is suitable. Work through two questions. First, what type of pathogen causes the illness? Second, is the aim to cure the disease or to ease the symptoms?
- Bacterial disease, aim to cure: an antibiotic that kills those specific bacteria.
- Viral disease, aim to cure: an antibiotic will not work, and it is difficult to make drugs that kill viruses without damaging the body's tissues. The body's immune system has to do the work.
- Any disease, aim to ease the symptoms: a painkiller or another medicine that treats symptoms, such as pain or a high temperature.
Notice that these medicines can be used together. A patient with a bacterial ear infection might take an antibiotic to kill the bacteria and a painkiller to ease the earache while the antibiotic does its job.
Worked example
A patient has a bacterial chest infection and a painful cough. Which medicines could help, and what does each one do?
An antibiotic, which kills the bacteria inside the body and cures the infection. A painkiller, which treats the symptom of pain but does not kill the bacteria.
Exam-style question
(a) Penicillin is an antibiotic. Describe what penicillin does in the body. [2 marks]
(b) A patient has the flu. Explain why the doctor does not prescribe an antibiotic. [2 marks]
(c) Explain why it is difficult to develop drugs that kill viruses. [2 marks]
Model answer
(a) It kills bacteria (1) that are inside the body, curing the bacterial disease (1).
(b) Flu is caused by a virus (1) and antibiotics cannot kill viral pathogens (1).
(c) Viruses reproduce inside body cells (1), so a drug that kills the virus is likely to damage the body's tissues too (1).
Exam tip
In a question about why an antibiotic is or is not used, always name the type of pathogen first (bacteria or virus), then say what antibiotics can do to it.