Antibiotics are medications used to treat – and, in some cases, prevent – bacterial infections.

They can be used to treat relatively mild conditions such as acne, as well as potentially life-threatening conditions such as pneumonia.

However, antibiotics often have no benefit for many other types of infection. Using them unnecessarily would only increase the risk of antibiotic resistance, so they are not routinely used.

Read more about when antibiotics are used.

How do I take antibiotics?

Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist.

Doses of antibiotics can be provided in several ways:

  • oral antibiotics – tablets, pills and capsules or a liquid that you drink, which can be used to treat most types of mild to moderate infections in the body
  • topical antibiotics – creams, lotions, sprays or drops, which are often used to treat skin infections
  • injections of antibiotics – these can be given as an injection or infusion through a drip directly into the blood or muscle, and are usually reserved for more serious infections

It's essential to finish taking a prescribed course of antibiotics, even if you feel better, unless a healthcare professional tells you otherwise. If you stop taking an antibiotic part way through a course, the bacteria can become resistant to the antibiotic.

Missing a dose of antibiotics

If you forget to take a dose of your antibiotics, take that dose as soon as you remember and then continue to take your course of antibiotics as normal.

However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

There is an increased risk of side effects if you have to take two doses closer together than normal.

Accidentally taking an extra dose

Accidentally taking one extra dose of your antibiotic is unlikely to cause you any serious harm.

However, it will increase your chances of experiencing side effects such as pain in your stomach, diarrhoea, and feeling or being sick.

If you accidentally take more than one extra dose of your antibiotic, are worried or experiencing severe side effects, speak to your GP or call NHS 111 as soon as possible.

Types of antibiotics

There are now hundreds of different types of antibiotics, but most of them can be broadly classified into six groups. These are outlined below.

  • penicillin – widely used to treat a variety of infections, including skin infections, chest infections and urinary tract infections
  • cephalosporins – can be used to treat a wide range of infections, but are also effective for treating more serious infections, such as septicaemia and meningitis
  • aminoglycosides – tend to only be used to treat very serious illnesses such as septicaemia, as they can cause serious side effects, including hearing loss and kidney damage; they break down quickly inside the digestive system, so they have to be given by injection, but are also used as drops for some ear or eye infections
  • tetracyclines – can be used to treat a wide range of infections; commonly used to treat moderate to severe acne and rosacea, which causes flushing of the skin and spots
  • macrolides – can be particularly useful for treating lung and chest infections; can also be a useful alternative for people with a penicillin allergy or to treat penicillin-resistant strains of bacteria
  • fluoroquinolones – broad-spectrum antibiotics that can be used to treat a wide range of infections

Side effects

As with any medication, antibiotics can cause side effects. Most antibiotics don't cause problems for people who take them if they're used properly, and serious side effects are rare.

The most common side effects of antibiotics include:

  • being sick
  • feeling sick
  • bloating and indigestion
  • diarrhoea

Around 1 person in 15 has an allergic reaction to antibiotics, especially penicillin and cephalosporins. In very rare cases, this can lead to a serious allergic reaction (anaphylaxis), which is a medical emergency.

Read more about the side effects of antibiotics.

Considerations and interactions

Some antibiotics are not suitable for people with certain medical conditions, or women who are pregnant or breastfeeding. You should only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member.

Some antibiotics can also react unpredictably with other medications, such as the oral contraceptive pill and alcohol. It is therefore important to read the information leaflet that comes with your medication carefully.

Read more information about: 

Antibiotic resistance

Both the NHS and health organisations across the world are trying to reduce the use of antibiotics, especially for conditions that are not serious.

This is to try to combat the problem of antibiotic resistance, which is when a strain of bacteria no longer responds to treatment with one or more types of antibiotics.

Antibiotic resistance can occur in several ways. Strains of bacteria can change (mutate) and, over time, become resistant to a specific antibiotic. The chance of this increases if a person does not finish the course of antibiotics they have been prescribed, as some bacteria may be left to develop resistance.

Antibiotics can also destroy many of the harmless strains of bacteria that live in and on the body. This allows resistant bacteria to multiply quickly and replace them.

The overuse of antibiotics in recent years has played a major part in antibiotic resistance. This includes using antibiotics to treat minor conditions that would have got better anyway.

It has led to the emergence of "superbugs". These are strains of bacteria that have developed resistance to many different types of antibiotics. They include:

These types of infections can be serious and challenging to treat, and are becoming an increasing cause of disability and death across the world. The World Health Organization (WHO) estimates there are around 170,000 deaths related to MDR-TB each year.

The biggest worry is new strains of bacteria may emerge that cannot be effectively treated by any existing antibiotics.

Carbapenemase-producing Enterobacteriaceae are one such emerging group of bacteria, with several types. These bacteria are widespread in some parts of the world, including parts of Europe, and are beginning to be seen in the UK.

Read more about how you can help prevent the progression of antibiotic resistance.

The Tokkels - antibiotics

Antibiotics help fight infection caused by bacteria. In this animation the Tokkels learn that antibiotics do not help against viral infections such as cold and flu.

Media last reviewed: 19/07/2014

Next review due: 19/07/2016

How do antibiotics work?

Antibiotics work in one of two ways:

  • they kill bacteria by disrupting one of the processes they need to survive, such as turning glucose into energy
  • they prevent bacteria reproducing and spreading – for example, by disrupting the processes bacteria use to produce new cells, such as growing new proteins

Read answers to some common questions about antibiotics.

Page last reviewed: 05/06/2014

Next review due: 05/06/2016