Some important considerations associated with the six main classes of antibiotics are listed below.


Do not take penicillins if you previously had an allergic reaction to them. People with a history of allergies, such as asthma, eczema or hay fever, are at higher risk of developing a serious allergic reaction (anaphylaxis) to penicillins. These reactions are rare, however.

Patients who are allergic to one type of penicillin will be allergic to all of them, as the allergy is related to the basic structure of the antibiotic.

Penicillin may not be suitable if you have:

Pregnancy and breastfeeding

Most penicillins can be used during pregnancy and breastfeeding in the usual doses.

Tell your healthcare professional if you are pregnant or breastfeeding so they can prescribe the most suitable antibiotic for you.


If you previously had an allergic reaction to penicillin, you may also be allergic to cephalosporins.

Cephalosporins may not be suitable if you have kidney disease. If the professional in charge of your care does decide to prescribe cephalosporins, it will probably be at a lower dose.

You should never take a cephalosporin if you have acute porphyria, a genetic condition that can cause skin and nerve problems.

Cephalosporins are thought to be safe to take during pregnancy, but as a precaution they are only ever used if the benefits of treatment are thought to outweigh potential risks.

Cephalosporins are not recommended for women who are breastfeeding.


Aminoglycosides are normally only used to treat life-threatening conditions such as septicaemia, as they can cause kidney damage in people with pre-existing kidney disease.

They are only used during pregnancy if your doctor believes they are essential.


The use of tetracyclines is not usually recommended unless absolutely necessary in the following groups:

  • people with kidney disease – except doxycycline, which can be used
  • people with liver disease
  • people with the autoimmune condition lupus, which can cause skin problems, joint pain and swelling, and fatigue (feeling tired all the time)
  • children under the age of 12
  • pregnant or breastfeeding women


You should not take macrolides if:

  • you have porphyria – a rare inherited blood disorder
  • you have a heart rhythm disorder or you're at risk of developing one – such as atrial fibrillation, where the heart beats abnormally fast

You should not take a type of macrolide called telithromycin if you have myasthenia gravis, which is an uncommon condition that causes muscle weakness.

If you're pregnant or breastfeeding, the only type of macrolide you can take is erythromycin (Erymax, Erythrocin, Erythroped or Erythroped A).

Erythromycin can be used at the usual doses throughout your pregnancy and while you're breastfeeding.

Other macrolides should not be used during pregnancy unless advised by a specialist.


Fluoroquinolones are not suitable for women who are pregnant or breastfeeding.

Medicine guide

Find information about a specific medication on our antibiotic medicine guide.

Page last reviewed: 05/06/2014

Next review due: 05/06/2016