There are some important things to consider before taking antibiotics.

This page contains information on the six main classes of antibiotics:








Don't take one of the penicillin-based antibiotics if you've had an allergic reaction to them in the past. People who are allergic to one type of penicillin will be allergic to all of 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, although cases are rare.

Penicillins may need to be used at lower doses and with extra caution 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're pregnant or breastfeeding, so they can prescribe the most suitable antibiotic for you.


If you previously had an allergic reaction to penicillin, there's a chance that you may also be allergic to cephalosporins.

Cephalosporins may not be suitable if you have kidney disease, but if you need one you will probably be given a lower than usual dose.

If you're pregnant or breastfeeding, or have acute porphyria, check with your doctor, midwife or pharmacist before taking cephalosporins.


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

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


The use of tetracyclines isn't 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 shouldn't take macrolides if you have porphyria – a rare inherited blood disorder.

If you're pregnant or breastfeeding, the only type of macrolide you can take is erythromycin (Erymax, Erythrocin, Erythroped or Erythroped A) unless a different antibiotic is recommended by your doctor.

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

Other macrolides shouldn't be used during pregnancy, unless advised by a specialist.


Fluoroquinolones aren't normally suitable for women who are pregnant or breastfeeding.

Page last reviewed: 09/06/2016

Next review due: 09/06/2018