Metronidazole Use During Breastfeeding
Yes, a breastfeeding patient can take metronidazole, as it is considered "possibly safe" and compatible with breastfeeding according to current guidelines, though specific precautions should be followed based on dosing regimen. 1
Guideline Recommendations
Metronidazole can be used during lactation if there are no other safer alternatives. 1 The European Respiratory Society/Thoracic Society of Australia and New Zealand (ERS/TSANZ) classifies metronidazole as "possibly safe" for breastfeeding, while the American Academy of Dermatology suggests it as safe based on cohort study evidence showing no significant adverse effects in infants. 1, 2
Dosing-Specific Precautions
The key consideration is the dose and duration of metronidazole therapy:
For single high-dose therapy (2 g oral dose): Stop breastfeeding for 12-24 hours after the dose to minimize infant exposure. 1, 3
For standard therapeutic doses (400 mg three times daily or 600-1200 mg/day): Breastfeeding can continue without interruption, as studies demonstrate no serious adverse reactions in infants at these doses. 4, 5
Pharmacokinetic Data
Metronidazole is present in breast milk at concentrations similar to maternal plasma, with a milk-to-plasma ratio of approximately 0.9-1.0. 4, 6
Mean milk concentrations around peak levels are approximately 15.5 micrograms/mL following 400 mg doses three times daily. 4
Infant plasma concentrations range from 1.27-2.41 micrograms/mL, representing approximately 15% of maternal plasma levels by body weight. 4, 6
Maximum estimated infant intake is approximately 3.0 mg/kg/day assuming 500 mL daily milk consumption. 6
Safety Evidence
No significant adverse effects have been documented in breastfed infants whose mothers received metronidazole. 4 A study of 35 infants monitored for adverse reactions to maternal metronidazole therapy (400 mg three times daily in combination with other antibiotics) found no significant increases in adverse effects attributable to metronidazole compared to control groups. 4
Important Caveats
FDA labeling caution: The FDA drug label notes that metronidazole has shown carcinogenic activity in rodent studies and states "a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother." 7 However, this represents older, conservative guidance that conflicts with more recent clinical evidence and guideline recommendations.
Long-term maternal therapy: If the mother requires prolonged metronidazole treatment, there is a theoretical risk of neonatal bleeding due to inhibition of vitamin K synthesis, though this has not been confirmed in clinical practice. 1
Infant monitoring: Breastfed infants should be monitored for gastrointestinal effects due to potential alteration of intestinal flora. 2
Antibiotic interference: Metronidazole in breast milk could potentially cause falsely negative cultures if the breastfed infant develops a fever requiring evaluation. 2
Clinical Context
Metronidazole is commonly used during breastfeeding for conditions including:
- Pouchitis 1
- Perianal Crohn's disease 1
- Intra-abdominal abscesses from fistulizing Crohn's disease 1
- Hidradenitis suppurativa 1
- Trichomoniasis 3
For trichomoniasis specifically, the single 2 g dose regimen with 12-24 hour breastfeeding interruption is the preferred approach. 1, 3