All penicillin antibiotics can be used during breastfeeding with precautionary infant monitoring. Recommendations apply to full term, healthy infants.

General considerations

It is important to complete an individual risk assessment for your patient and to apply the principles of prescribing in breastfeeding when looking at the available information and making treatment decisions.

Many other antibiotics can also be considered in breastfeeding. See our specific guidance on chloramphenicol, metronidazole, and nitrofurantoin.

Choice of penicillin

All penicillin antibiotics 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.

The 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.

Combination preparations

Some penicillins are combined with beta-lactamase inhibitors such as clavulanic acid (co-amoxiclav) or tazobactam (combined with piperacillin as Tazocin®), which help to minimise the risk of antimicrobial resistance. Although there is no information on how much passes into breastmilk, studies have not identified any concerns for their use in breastfeeding.

Breast milk levels

There is limited published evidence of use in breastfeeding. Studies for amoxicillin, ampicillin, benzylpenicillin (penicillin G), flucloxacillin, phenoxymethylpenicillin (penicillin V) and piperacillin show negligible levels in breast milk.

There is no published information for pivmecillinam or temocillin, however breast milk levels are expected to be low.

Infant levels

There is very limited evidence of infant levels after being exposed to a penicillin antibiotic via breast milk.

A study of eight infants exposed to ampicillin in breast milk detected ampicillin in the urine of two infants. A further study analysed the urine of two infants exposed to phenoxymethylpenicillin through breast milk; only one infant had a detectable level.

Infant Effects

Infant side effects

Episodes of transient diarrhoea and thrush were reported in some studies. There has also been the occasional case report of rash, nausea, irritability and drowsiness; these were usually mild and self-limiting, and could be attributable to other causes.

Infant monitoring

As a precaution, monitor for gastro-intestinal disturbances, oral candida infection, hypersensitivity reactions (including rashes or breathing problems), nausea, irritability, and drowsiness.

Precautionary infant monitoring will quickly pick up any potential issues. Further investigation is usually required before any issues or side effects can be attributed to the medicine.

Oral and gut microflora

Exposure to antimicrobials can affect the infant’s natural balance of microflora. In rare cases, antibiotic exposure has disturbed this balance and caused gastrointestinal disturbances or candidiasis. These effects are generally mild and resolve upon treatment discontinuation.

Treatment of infant infections

There is no conclusive information on whether the concentrations the infant is exposed to through breast milk are enough to be bactericidal or cause bacterial resistance.

If the infant needs treatment themselves with a penicillin or other antibiotic, they should receive the appropriate infant therapeutic dose, regardless of concomitant exposure through breast milk.


There is a theoretical risk of hypersensitivity in the infant after exposure to penicillins through breast milk. Foetal exposure to antibiotics through the placenta may cause sensitisation. Further exposure may result in allergic reactions, even from the negligible quantities seen in breast milk. As a precaution, the infant should be monitored for signs of hypersensitivity which includes rashes and breathing problems.

Patient Information

The NHS website provides advice for patients on the use of specific medicines in breastfeeding.

Further Advice

Get in touch with the UK Drugs In Lactation Advisory Service (UKDILAS), our specialist breastfeeding medicines advice service, if:

  • the infant is unwell or premature
  • multiple medicines are being taken
  • the medicine in question is not included in our advice
  • the medicine will be taken long-term
  • you need further advice

About our recommendations

Recommendations are based on published evidence where available. However, evidence is generally very poor and limited, and can require professional interpretation. Assessments are often based on reviewing case reports which can be conflicting and lack detail.

If there is no published clinical evidence, assessments are based on: pharmacodynamic and pharmacokinetic principles, extrapolation from similar drugs, risk assessment of normal clinical use, expert advice, and unpublished data. Simulated data are now increasingly being used due to the ethical difficulties around gathering good quality evidence in this area.


Full referencing is available on request.