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Respiratory Tract Infection Resource for Patients

How Antibiotics Work

In a healthy person, the body’s immune system destroys harmful bacteria before they can multiply and cause symptoms. Even when symptoms do occur, the immune system can usually fight the infection effectively.

Sometimes, however, our bodies need help from antibiotics to fight infection. There are many different types of antibiotic but they all work in one of two ways:

  • Bactericidal antibiotics kill the bacteria in some way, for example by interfering with the formation of the cell walls
  • Bacteriostatic antibiotics prevent the bacteria from growing and multiplying
Action of antibiotics – both bactericidal (penicillins and cephalosporins) and bacteriostatic (most other antibiotics)

Figure 1 Action of bactericidal and bacteriostatic antibiotics

If antibiotics are overused, or used incorrectly, there is a chance that the bacteria will become resistant and the antibiotic will fail to cure the infection.

The information provided on this website does not replace a consultation with a medical professional. If you have any concern about your condition please contact a medical professional.












  • MYTHS AND FACTS
  • Myth: If a prescribed antibiotic didn’t work before, it won't work now.

    Fact: Even if a prescribed antibiotic didn’t work last time, it may work for this infection. There are two reasons for this. The first is that different antibiotics target specific types of bacterial infections and may not have been effective against the type of bacteria that caused your infection last time.

    Another reason that your prescribed antibiotics did not seem to work last time could be that your previous infection was viral not bacterial. Antibiotics are only effective against bacterial infections. If the infection you have now is bacterial, the right type of prescribed antibiotic will be effective.

  • FAQ
  • Q: What if I miss a dose of antibiotics?

    A: Missing a dose means that the level of antibiotic in your bloodstream is reduced – this reduces its effectiveness.

    If you miss a dose you should read the patient information leaflet (PIL) that came with your prescription. The PIL is produced by the manufacturer and gives you advice about what you should do next. If you have lost your PIL your pharmacist should be able to give you another one.

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