Healthdirect Free Australian health advice you can count on.

Medical problem? Call 1800 022 222. If you need urgent medical help, call triple zero immediately

healthdirect Australia is a free service where you can talk to a nurse or doctor who can help you know what to do.

Antibiotics work against bacteria.

Antibiotics work against bacteria.
beginning of content


4-minute read

What are antibiotics?

Antibiotics are medicines that treat infections and diseases caused by bacteria. Antibiotics damage bacteria so the body’s immune system can fight them. They do not work against viruses.

Different antibiotics work against different bacteria. Penicillin is an example of an antibiotic. Sometimes, doctors choose an antibiotic based on what they believe will work. At other times, doctors will perform tests to work out which bacteria are causing the infection, and which antibiotics are likely to be effective against them.

Many antibiotics are less effective than they once were due to them being used so often and bacteria becoming resistant to their effects. This is called antibiotic resistance. Antibiotics should only be used if they are needed to treat a bacterial infection.

Allergic reaction to antibiotics

If you are allergic to antibiotics, you may get signs and symptoms like a rash, swelling of the face or difficulty breathing.

Anaphylaxis is a severe allergic reaction, and usually occurs within an hour of taking an antibiotic. A severe allergic reaction is a medical emergency requiring immediate medical attention. You may need to call triple zero (000) and perform first aid.

The symptoms of anaphylaxis are:

  • difficult/noisy breathing
  • swelling of the tongue
  • swelling/tightness of the throat
  • difficulty talking/hoarse voice
  • wheezing or coughing
  • dizziness or collapse
  • pale and floppy (especially young children)

Sometimes you can get less dangerous symptoms before an anaphylaxis, such as:

If you are allergic to antibiotics you may be instructed by a doctor how to avoid triggers and if severe they may instruct you how to use an adrenaline autoinjector such as EpiPen®. The doctor will record the allergy and type of reaction in your notes and electronic health records and will give you an anaphylaxis action plan. You may be advised to wear an emergency ID.

Most allergies are caused by penicillin or antibiotics closely related to penicillin, or by another type of antibiotic called sulfonamides, but any antibiotic could cause an allergy. If you are allergic to one antibiotic in a class, you are likely to be allergic to all other antibiotics in that class.

Feeling nauseous and vomiting after taking antibiotics is a common side-effect of the medicine, rather than an allergic reaction.

Your doctor can usually diagnose allergic reactions to antibiotics by talking to you. They may refer you to an allergy specialist, who may ask for skin allergy and blood tests.

If you have any other concerns about antibiotics, including possible side effects, contact your doctor.

What is antibiotic resistance?

Many bacterial infections are treated with antibiotics. Sometimes the bacteria change to protect themselves against the antibiotic. When this happens the antibiotic no longer works. This is called antibiotic resistance and is a serious global problem.

The more bacteria are exposed to antibiotics, the more chances they have to change and become resistant. If you use antibiotics when they’re not needed or don’t take antibiotics properly — such as missing doses or not completing the course — you give bacteria opportunities to become resistant.

If an antibiotic no longer works against the resistant bacteria:

  • infections take longer to heal
  • infections can get worse and lead to more serious problems
  • infections are more likely to spread to other people. Because bacteria are resistant, the antibiotic may not work for other people, further spreading the problem

Sometimes it is possible to use another antibiotic to which bacteria aren’t resistant. However, it may not work as well, and it could have side effects. Also, bacteria may eventually become resistant to this antibiotic too.

For these reasons, antibiotic resistance is a major threat to human health. There is concern that in time, there’ll be bacterial infections that just can’t be treated.

What are ‘superbugs’?

‘Superbugs’ are bacteria that are difficult to treat because they are resistant to several different antibiotics, and especially those that treat other resistant bacteria.

Superbugs such as Methicillin-resistant Staphylococcus aureus (MRSA) and multi-drug-resistant strains of Escherichia coli (E. coli) are becoming more common, and can be a real problem in hospitals.

How can I help prevent antibiotic resistance?

Antibiotic resistance can’t be totally stopped, but it can be slowed down by sensibly using antibiotics. You can help by:

  • not taking antibiotics for a cold or the flu, including cough and sore throat; viruses cause most colds, and antibiotics don’t work against viruses
  • telling your doctor you only want antibiotics when necessary — such as for serious bacterial infections like pneumonia
  • taking your antibiotic as prescribed, and completing the full course, even if you start to feel better
  • never saving antibiotics for the next time you’re sick
  • never taking antibiotics prescribed for someone else
  • having good hygiene practices to avoid spreading infections

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: May 2020

Back To Top

Need more information?

These trusted information partners have more on this topic.

Top results

Antibiotic resistance: what you need to know | Children’s Health Queensland

Imagine a future world where a case of tonsillitis could be life-threatening but there is nothing their doctor can do because antibiotics no longer work.

Read more on Queensland Health website

Antibiotics, antibiotic resistance and childhood respiratory tract infections - NPS MedicineWise

Antibiotic resistance is a growing problem in Australia. What can parents do to manage common childhood respiratory tract infections without antibiotics?

Read more on NPS MedicineWise website

The Rise of the Superbugs: The global threat of antimicrobial resistance | HealthEngine Blog

What is the problem and how much of a problem is it? The year 1928 set the scene for one of the most significant public health milestones in history – the discovery of penicillin

Read more on HealthEngine website

Antibiotics and children -

Antibiotics: what are they and when does my child need them? Also, how to use antibiotics correctly and side effects of antibiotics.

Read more on myDr website

Non-Specific Urethritis - what it is, how to prevent it, and how to treat it

Non-Specific Urethritis (NSU) is the swelling of the urethra and can be treated with a course of antibiotics.

Read more on NSW Health website

The facts about Gonorrhoea - what it is, how to prevent it, how to treat it

Gonorrhoea is sometimes called ‘Gono’ and can be easily treated with a course of antibiotics if caught early. Regular STI testing and condom use helps protect against Gonorrhoea.

Read more on NSW Health website

Mycoplasma Genitalium - what it is, how to prevent it, and how to treat it

Mycoplasma Genitalium is an emerging STI, very similar to Chlamydia. Read this for everything that you need to know about Mycoplasma Genitalium and how to prevent it and treat it.

Read more on NSW Health website

Antibiotics -

Antibiotics attack bacteria - germs responsible for certain infections. Each antibiotic attacks different types of bacteria and will be useful for treating particular infections.

Read more on myDr website

Colds: commonsense not antibiotics -

If you have a cold, commonsense self-care measures and over-the-counter medicines can help to relieve symptoms. Antibiotics are not helpful in treating the common cold, which is caused by a virus.

Read more on myDr website

ACD A-Z of Skin - Tetracyclines

Tetracyclines are a class of antibiotics (including tetracycline, doxycycline and minocycline) which are used to treat skin infections.

Read more on Australasian College of Dermatologists website

Healthdirect 24hr 7 days a week hotline

24 hour health advice you can count on

1800 022 222

Government Accredited with over 140 information partners

We are a government-funded service, providing quality, approved health information and advice

Australian Government, health department logo ACT Government logo New South Wales government, health department logo Northen Territory Government logo Government of South Australia, health department logo Tasmanian government logo Victorian government logo Government of Western Australia, health department logo

Healthdirect Australia acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to land, sea and community. We pay our respects to the Traditional Owners and to Elders both past and present.