Antibiotics illustration

Antibiotics save lives, but resistance to them is increasing. Dr Nicholas Brown, Consultant Medical Microbiologist at Addenbrooke’s Hospital, Cambridge, tells Christopher Allen when you need them and when you don’t.

Antibiotics treat a range of bacterial infections. They work in one of two ways: killing bacteria by disrupting functions they need to survive, or preventing bacteria from multiplying by disrupting processes they use to make cells. It’s vital you only take antibiotics when you need them.

Why have I been given an antibiotic?

Your doctor has prescribed antibiotics because they suspect or have confirmed you have a bacterial infection. GPs are most likely to prescribe them for respiratory infections (such as pneumonia), a urine infection or a skin or soft tissue infection (such as a cut or other wound).

Most bacterial infections clear up quickly. Severe infections are more likely in hospital, where existing illness makes people more vulnerable. There is also a higher risk of infection following surgery or if you have a device such as a drip, catheter or drain inserted.

Sometimes, antibiotics are given through an injection or drip, rather than in tablet form.

What type of antibiotic will I be given?

This depends on the infection location and type of bacteria involved. You need a high concentration of antibiotic at the infection site. So, for a urine infection, you’ll be given an antibiotic that passes through the kidneys and gets to the urine.

The most common tablet antibiotics are the penicillin family of drugs (such as amoxicillin and flucloxacillin). Antibiotics may also be given as cream, ointment or drops.

My GP won’t give me an antibiotic even though I am unwell. Why?

Antibiotics are only active against bacteria; viral illnesses such as colds, flu and most coughs won’t respond to them. Many infections go away without antibiotics if you look after yourself with rest and paracetamol, or with help from your pharmacist.

Taking antibiotics when you don’t need them can mean they lose their ability to kill bacteria.

There are times when you should seek medical help. These include: if you have a fever plus a rash that doesn’t fade when a glass is pressed against it; a hoarse voice or cough lasting more than three weeks; coughing up blood; and, if you have a wound, increased redness around it, or pus, blood or a smell coming from it.

I’ve had a lot of antibiotics before. Does this mean they won’t work?

Antibiotics are only active against bacteria; viral illnesses such as colds, flu and most coughs won’t respond to them

Bacteria can evolve in ways that allow them to resist the effects of antibiotics. If so, the cause of the infection becomes more difficult to treat. To avoid this, it’s important that antibiotics are only prescribed when absolutely necessary.

How does my doctor know what type of bacteria is causing the infection?

They might be able to tell from your symptoms, or they might prescribe a ‘broad-spectrum’ antibiotic.

Sometimes a culture is taken to find which bacteria are causing your infection. The culture may be a sample of mucus, blood or urine, or a swab of a wound.

This is more common in hospitals but is now being recommended in GP surgeries too, especially when an initial course of antibiotics isn’t effective.

What are the possible side effects?

The most common side effects are stomach upset, feeling nauseous or diarrhoea. This is usually mild and doesn’t mean you should stop taking antibiotics.

However, if your symptoms are severe or persistent, seek advice from your GP. Some people develop a rash, which should always be checked by your GP and may mean that you will need a different antibiotic.

Can I take antibiotics with my heart medication?

Yes you can. Some antibiotics can affect how warfarin and statins work but that can be monitored. Before your GP prescribes antibiotics, and before your pharmacist dispenses them, your other medications will be checked to make sure there aren’t any serious interactions.

Is there any food or drink I should avoid?

For most antibiotics, this isn’t a problem, but your GP or pharmacist can give specific advice. Check the label of your medications to see if you should take them before, with or after food.

What about allergies?

Around one person in 15 has an allergic reaction to antibiotics, especially the penicillin family. In most cases, the allergic reaction is mild, causing an itchy rash, but you should see a doctor. A severe allergic reaction is very rare. If facial swelling and breathing difficulties occur, call 999.

How long should I take them for?

It’s vital that you complete the full course prescribed by your GP, even if you begin to feel better. If you stop early, it’s more likely the infection will return and you’ll need a further course of antibiotics. This will increase your chances of developing antibiotic resistance.

Dr Nicholas BrownCV Dr Nicholas Brown

  • Consultant Medical Microbiologist, Addenbrooke’s Hospital, Cambridge
  • Associate Lecturer, University of Cambridge
  • Former President of the British Society for Antimicrobial Chemotherapy (BSAC) and is involved with its initiative to improve awareness about antibiotic resistance
  • Member of groups overseeing implementation of the Department of Health strategy to combat antibiotic resistance

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