Introduction of Antibiotics

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 (a type of lung infection).

Read more about when antibiotics are used.

How do I take antibiotics?

Doses of antibiotics can be provided in several ways:

  • oral antibiotics – tablets, pills and capsules or a liquid that you drink
  • topical antibiotics – creams, lotions, sprays or drops
  • injections of antibiotics – they can be given as an injection, or an infusion through a drip, directly into the blood or a muscle

How the antibiotic is given will depend on the type of infection. Topical antibiotics are often used to treat skin infections while oral antibiotics can be used to treat most types of mild to moderate infections in the body. Antibiotic injections are usually reserved for more serious infections and are often given in hospital.

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 (see below).

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 is widely used to treat certain infections such as skin infections, chest infections and urinary tract infections.

Some widely used types of penicillin include:

Around 1 in 15 people will have an allergic reaction after taking penicillin and a very small number of people will develop a severe allergic reaction (anaphylaxis).

It’s important to let your doctor or the health professional treating you know if you think you may be allergic to penicillin.

Another problem with penicillin is that some strains of bacteria have become resistant to it because it has been so widely used.


Cephalosporins are broad-spectrum antibiotics, which means they are effective in treating a wide range of different types of infections including more serious infections, such as:

  • septicaemia – infection of the blood
  • pneumonia
  • meningitis – infection of the outer protective layer of the brain and spinal cord

Examples of cephalosporins include:

If you are allergic to penicillin you may also be allergic to cephalosporins.


Aminoglycosides are a type of antibiotic that used to be widely prescribed until it was found that they could cause both damage to hearing and the kidneys. Because of this, they tend now to be used only to treat very serious illnesses such as meningitis.

Aminoglycosides break down quickly inside the digestive system so they have to be given by injection or as ear or eye drops. The most widely used aminoglycoside in England is called gentamicin.


Tetracyclines are another type of broad-spectrum antibiotic that can be used to treat a wide range of infections.

They are commonly used to treat severe acne and a condition called rosacea, which causes flushing of the skin and spots.


Macrolides are a type of antibiotic that 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.

Examples of macrolides include:


Fluoroquinolones are the newest type of antibiotic. They are broad-spectrum antibiotics that can be used to treat a wide range of infections.

Examples of fluoroquinolones are:

Side effects

Most antibiotics (with the exception of the aminoglycosides) don’t cause problems for people who take them and serious side effects are rare. The most common reported side effects of antibiotics are:

  • being sick
  • feeling sick
  • indigestion
  • diarrhoea 

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 and the oral contraceptive pill. It is therefore important to read the information leaflet that comes with your medication carefully.

Read more about things to consider with antibiotics and things that interact with antibiotics.

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 so-called ‘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. For example, the World Health Organization (WHO) estimates that there are around 150,000 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.

There are already signs of this with the emergence of a type of bacteria called New Delhi metallo-beta-lactamase (NDM-1), which appears to be highly resistant to treatment.

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

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