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 and 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 is 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.

If you have to take two doses closer together than normal, there is an increased risk of side effects.

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, or if you are worried or are 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 are 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 in treating more serious infections such as septicaemia and meningitis.
• Aminoglycosides tend to be used only 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. They are also used as drops for some ear or eye infections.
• Tetracyclines can be used to treat a wide range of infections. They are commonly used to treat moderate to severe acne and a condition called rosacea, which causes flushing of the skin and spots.
• Macrolides can be particularly useful in treating lung and chest infections. They can also be a useful alternative for people with a penicillin allergy or to treat penicillin-resistant strains of bacteria.
• Fluoroquinolones are broad-spectrum antibiotics that can be used to treat a wide range of infections.

For detailed information about a specific antibiotic, see our antibiotic medicine guide page.

Side effects

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

The most common side effects of antibiotics include:

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

Around one 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 for women who are pregnant or breastfeeding. You should only ever take antibiotics that are prescribed to you – never 'borrow' them from a friend of family member.

Some antibiotics can also react unpredictably with other medications, for example, 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: 

• things to consider before taking antibiotics
• how antibiotics interact with other medicines

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 mutate (change) and, over time, become resistant to a specific antibiotic. The chance of this increases if a person does not finish the course of antibiotics as some bacteria may be left to develop resistance.

Also, antibiotics can 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:

• meticillin-resistant Staphylococcus aureus (MRSA) 
• Clostridium difficile (C. diff)
• the bacteria that cause multi-drug-resistant tuberculosis (MDR-TB)
• CPE (Carbapenemase-producing Enterobacteriaceae)

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

The biggest worry is that there may emerge new strains of bacteria that are effectively untreatable 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 further progression of antibiotic resistance.