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

Penicillin

Do not take penicillins if you have had a previous 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. However, such reactions are rare.

Patients who are allergic to one type of penicillin will be allergic to all (the allergy is related to the basic penicillin structure).

Penicillin may not be suitable if you:

• have severe kidney disease
• have liver disease

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.

Cephalosporins

If you have had a previous 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

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.

Tetracyclines

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

Macrolides

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 are pregnant or are 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 are breastfeeding.

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

Fluoroquinolones

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