Metronidazole can be used during breastfeeding for most usual treatment courses. 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.


Oral / intravenous / rectal use

Short courses of oral, intravenous or rectal metronidazole are considered to be compatible with breastfeeding, but infant monitoring is recommended.

No interruption of breastfeeding is required, even after 2g oral doses (as a single dose, or daily for a three-day course).

If use is required for longer than a few weeks, contact our specialist service for further advice.

Topical use, including intravaginal gel

Metronidazole can be used topically during breastfeeding. This includes the intravaginal gel.

When applying creams or gel, ensure the infant does not come into contact with treated areas of skin. Wash hands thoroughly after application.

Clinical considerations

The concentrations of metronidazole found in breast milk are insufficient to have a bactericidal effect in the infant; therefore an infant with an active infection needs independently treating in their own right.

Evidence relating to the excretion of metronidazole in breast milk is relatively old and of poor quality. However, metronidazole has been used widely during breastfeeding for many years, with few reports of infant side-effects.

Excretion into breastmilk

Metronidazole has a low molecular weight, and very low protein binding (less than 20%); properties which make transfer into breast milk more likely. Published evidence shows that it passes into breast milk in moderate amounts.

The oral bioavailability of metronidazole is almost complete, which means that the infant will absorb the majority they are exposed to in breast milk.

However, metronidazole and its active metabolite hydroxymetronidazole, have relatively short half-lives, therefore drug accumulation in the breastfed infant is unlikely. This reduces the risk of infant side-effects.

Infant effects

No side effects were reported in the majority of infants exposed to metronidazole in breast milk.

In one study, 35 newborn infants were exposed to metronidazole in breast milk (doses and administration routes not stated). There was an increase in loose stools and one case of oral thrush, but no increase in nappy rash, feeding problems, or poor weight gain up to the time of discharge.

Taste of breast milk

It has been suggested that metronidazole might make breast milk taste bitter, leading to poor feeding. This is largely anecdotal and not supported by published evidence. It may, however, be related to the common side-effect of ‘metallic taste’ found with normal therapeutic use.

No established carcinogenic risk

Historically, metronidazole has been contraindicated during breastfeeding due to concerns about mutagenic or carcinogenic effects, based on data from animal studies.

The balance of current evidence, clinical experience, and the consensus of specialist opinion, is that there is no established mutagenic or carcinogenic risk to humans, including infants exposed through breast milk.

Specific route recommendations

Patient Information

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

Contact us

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

  • you need further advice
  • the medicine in question is not included here
  • the infant is unwell or premature
  • multiple medicines are being taken

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 is now increasingly being used due to the ethical difficulties around gathering good quality evidence in this area.


Full referencing is available on request.