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
Use with caution
Short courses of oral metronidazole, can be used during breastfeeding, but infant monitoring is required. If longer term use is required, contact our specialist service for further advice.
Infant monitoring
Although side effects are unlikely, as a precaution, monitor the infant for:
poor feeding and adequate weight gain
gastro-intestinal disturbances including vomiting and diarrhoea
oral candida
irritability
rash, due to the theoretical concern of hypersensitivity.
Monitoring the infant will quickly pick up any potential issues, but usually further investigation is required before the cause can be identified. If a side effect is suspected, contact a healthcare professional for further advice.
Further information
Published evidence shows that oral metronidazole doses of up to 400mg three times daily, produce moderate milk levels. Metronidazole and hydroxymetronidazole were detectable in the serum of most of the exposed infants. However, these infant serum levels are far lower than when metronidazole is used therapeutically in infants.
Use with caution
For some infections (e.g., bacterial vaginosis, urogenital trichomoniasis, or giardiasis), doses of 2g metronidazole are licensed, either as a single dose, or daily for a three-day course.
Breastfeeding may continue during treatment, but infant monitoring is required.
Infant monitoring
Although side effects are unlikely, as a precaution, monitor the infant for:
poor feeding and adequate weight gain
gastro-intestinal disturbances including vomiting and diarrhoea
oral candida
irritability
rash, due to the theoretical concern of hypersensitivity.
Monitoring the infant will quickly pick up any potential issues, but usually further investigation is required before the cause can be identified. If a side effect is suspected, contact a healthcare professional for further advice.
Further information
A small study showed that single doses of 2g oral metronidazole produced higher levels (24% of the weight adjusted maternal dose) in milk than those usually seen with low-dose oral therapy. However, with 2g daily doses taken for one to three days, the estimated total infant exposure is still lower than the daily dose used therapeutically in infants.
Interrupting breastfeeding to reduce infant exposure is not considered necessary.
Use with caution
Short courses of intravenous metronidazole can be used during breastfeeding, but infant monitoring is required.
Infant monitoring
Although side effects are unlikely, as a precaution, monitor the infant for:
Poor feeding and adequate weight gain
gastro-intestinal disturbances including vomiting and diarrhoea
oral candida
irritability
rash, due to the theoretical concern of hypersensitivity.
Monitoring the infant will quickly pick up any potential issues, but usually further investigation is required before the cause can be identified. If a side effect is suspected, contact a healthcare professional for further advice.
Further information
Pharmacokinetic studies have shown that plasma levels of oral and intravenous metronidazole are similar, due to the high oral bioavailability. Therefore similar milk levels would also be expected.
In a single-dose study, intravenous administration of 500mg metronidazole produced similar levels in breast milk to equivalent oral doses.
Use with caution
Short courses of rectal metronidazole can be used during breastfeeding, but infant monitoring is required.
Infant monitoring
Although side effects are unlikely, as a precaution, monitor the infant for:
Poor feeding and adequate weight gain
gastro-intestinal disturbances including vomiting and diarrhoea
oral candida
irritability
rash, due to the theoretical concern of hypersensitivity.
Monitoring the infant will quickly pick up any potential issues, but usually further investigation is required before the cause can be identified. If a side effect is suspected, contact a healthcare professional for further advice.
Further information
Metronidazole is readily absorbed following rectal administration, and the systemic bioavailability is relatively high. This means that passage into breast milk is likely.
A small study showed that rectal metronidazole (1g every 8 hours), produced similar milk levels to low dose oral metronidazole.
Topical or intravaginal metronidazole can be used during breastfeeding.
If clinically appropriate, topical routes of administration are usually preferred due to lower systemic concentrations, leading to lower concentrations in breast milk.
Infant monitoring
No specific infant monitoring is usually required. If a side effect is suspected, contact a healthcare professional for further advice.
Further information
Although there is no direct evidence for topical or intravaginal use of metronidazole during breastfeeding, systemic absorption is minimal and therefore milk levels will be negligible.
When applying creams or gel, ensure the infant does not come into contact with treated areas of skin. Wash hands thoroughly after application.
Patient Information
The NHS website provides advice for patients on the use of specific medicines in breastfeeding.
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.