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Antibiotic in pregnancy

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

During Pregnancy

Penicillins and Cephalosporins are drugs of choice in pregnancy and breastfeeding (1).

In pregnancy, avoid quinolones, tetracyclines, aminoglycosides, unless severe or life threatening infection, high dose metronidazole, trimethoprim (in first trimester - folate antagonist) and nitrofurantoin (at term - risk of neonatal haemolysis) (2).

BNF guidance with respect to antibiotic use in pregnancy states:

  • penicillins and cephaloridines are safe to use throughout pregnancy
  • sulphonamides interfere with the bile conjugating mechanism of the neonate, thus sulphonamides should be avoided if delivery is imminent
  • tetracylines should not be used in pregnancy. This group of drugs stain developing bone and teeth in the foetus. Also the use of tetracylines, when administered intramuscularly, has occasionally produced maternal liver failure
  • erythromycin - not known to be harmful
  • metronidazole - manufacturer advises avoidance of high-dose regimens
  • streptomycin may cause foetal auditory nerve damage
  • trimethoprim - this is safe after the first trimester. However, the sulphonamide warning applies for trimethoprim - sulphonamide preparations


Penicillins and Cephalosporins are drugs of choice in breastfeeding (1).

Penicillins in breastfeeding (3):

  • all penicillin antibitotics can be used during breastfeeding with precautionary infant monitoring
  • flucloxacillin, phenoxymethylpenicillin (penicillin V) and the broad-spectrum penicillins, such as amoxicillin and ampicillin, are the preferred choices as there is more evidence and experience to support their use
  • pharmacokinetic properties and characteristics of all the penicillins are very similar
    • although protein binding and bioavailability vary between the different penicillins, they are all acidic in nature and therefore only negligible quantities pass into milk
  • treatment choice should be primarily based on clinical indications and in line with national and local antimicrobial policy, with suitability in breastfeeding as a secondary consideration
    • ideally treatment should be at the lowest therapeutic dose for shortest duration of time

A review has stated (4):

  • Safe for administration:
    • aminoglycosides
    • amoxicillin
    • amoxicillin-clavulanate
    • antitubercular drugs
    • cephalosporins
    • macrolides
    • trimethoprim-sulphamethoxazole
    • trimethoprim - the BNF states that '..short-term use not known to be harmful'
  • Effects not known/to be used with caution:
    • chloramphenicol
    • clindamycin
    • dapsone
    • mandelic acid
    • nalidixic acid
    • nitrofurantoin - the BNF states '..avoid; only small amounts in milk but could be enough to produce haemolysis in G6PD-deficient infants..'
    • tetracyclines
  • Not recommended:
    • quinolones

Information about metronidazole and breast feeding is linked.

Note that the summary of product characteristics must be consulted before prescribing any drug in pregnancy and during breastfeeding.


  1. NHS Forth Valley. Empirical Antimicrobial Guidelines for Forth Valley Hospitals 2013-2015
  2. BNF Appendix 4:Pregnancy.
  3. NHS Specialist Pharmacy Service (February 16th 2024). Using penicillin antibiotics during breastfeeding
  4. Mathew JL. Effect of maternal antibiotics on breast feeding infants Postgrad Med J 2004;80:196-200.

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