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WebMD Medical Reference
Medically Reviewed by Dr Rob Hicks

Antibiotics are some of the most frequently prescribed medicines. They work by killing bacteria or preventing bacteria from multiplying and spreading. Antibiotics can be used to treat potentially life-threatening conditions such as pneumonia or other conditions such as acne.

Although antibiotics are useful in a wide variety of infections, it's important to understand that antibiotics only treat bacterial infections. Antibiotics are useless against viral infections such as the common cold, or fungal infections such as ringworm. Your GP can best decide if an antibiotic is right for your condition.

Types of antibiotics

There are many different types of antibiotics, but most can be broadly classified into six key groups:

What antibiotics are best for me?

Each antibiotic is effective only for certain types of infections, and your GP is best able to assess your needs and match them with the available medicines.

In most cases, a GP will choose an antibiotic based on the most likely cause of the infection. So, if you have an earache, and antibiotics are necessary, the doctor will choose the antibiotic that best combats the kind of bacteria linked to ear infections. A small number of bacteria cause about 90% of pneumonias, so if you are diagnosed with pneumonia, the doctor will choose an antibiotic that will kill those bacteria.

In some cases, your GP may use laboratory tests to make an antibiotic choice. Samples of mucus can be used to identify bacteria under the microscope and may help narrow down which species of bacteria is causing infection. Cultures may also be obtained for lab tests to identify the type of bacteria.

The number of doses and common side effects are also taken into account when choosing an antibiotic. Patterns of infection in your community may also be factored in. Some antibiotics are unsuitable for people with certain conditions, or for women who are pregnant or breastfeeding.

How are antibiotics taken?

Antibiotics come in various forms:

  • Oral: tablets and capsules or a liquid that you drink
  • Topical: creams, lotions, sprays or drops
  • Injections: injection by needle into the muscle, or an infusion through a drip directly into the blood

It is very important to take antibiotics correctly. Check the label to see the correct dose to take and how often. Ask your pharmacist if you have any questions.

Some medicines need to be taken with something in your stomach, such as a glass of milk or a few crackers. Others can only be taken with water. Taking your antibiotics incorrectly may affect their absorption and reduce their effectiveness.

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