Can you take sulfamethoxazole while breastfeeding?
What LactMed says
The National Library of Medicine’s own summary, quoted in full. We do not write a verdict of our own on this question, and we do not compress theirs into a label.
With healthy, fullterm infants it appears acceptable to use sulfamethoxazole during breastfeeding after the newborn period. The time of greatest risk for hemolysis in fullterm newborns without glucose-6-phosphate dehydrogenase (G6PD) deficiency might be as short as 8 days after birth. Until further data are accumulated, alternate agents should probably be used in jaundiced, ill, stressed or premature infants, because of the risk of bilirubin displacement and kernicterus. Sulfamethoxazole should be avoided while breastfeeding a G6PD deficient infant.
Quoted from Sulfamethoxazole — Drugs and Lactation Database (LactMed®), National Institute of Child Health and Human Development, revised November 15, 2024.
What LactMed would consider instead
LactMed ends this record by naming the drugs it would consider in place of sulfamethoxazole. Whether any of them fits depends on what you are treating — this is the database’s list, not a recommendation from us.
- Sulfisoxazole
- Trimethoprim-Sulfamethoxazole
How much sulfamethoxazole gets into breastmilk
Maternal Levels. Forty women who were 5 or fewer days postpartum period received oral co-trimoxazole equivalent to 800 mg of sulfamethoxazole twice daily. Another 10 women were given this dose three times daily. Milk levels were measured several times daily for 5 days. Average sulfamethoxazole levels were 4.5 and 5.3 mg/L, respectively, with the 2 dosages. With the usual dose of sulfamethoxazole 800 mg daily, an exclusively breastfed infant would be expected to receive 0.68 mg/kg daily of sulfamethoxazole. This is very low in comparison to the established treatment dosage 40 mg/kg daily for infants over 2 months of age.
Infant Levels. Relevant published information was not found as of the revision date.
What has been seen in breastfed infants
An extensive systematic review of the use of sulfonamides near term and during breastfeeding found no adverse reactions in infants. The authors concluded that use of sulfamethoxazole during breastfeeding presents no risk of neonatal kernicterus.
A prospective, controlled study asked mothers who called an information service about adverse reactions experience by their breastfed infants. Of 12 women who took sulfamethoxazole and trimethoprim during breastfeeding (time postpartum and dosage not reported), none reported diarrhea, drowsiness or irritability in her infant. Two mothers reported poor feeding in their infants.
Effects on milk supply
Relevant published information was not found as of the revision date.
Frequently asked questions
Can you take sulfamethoxazole while breastfeeding?
With healthy, fullterm infants it appears acceptable to use sulfamethoxazole during breastfeeding after the newborn period. The full record is quoted on this page, and the decision is one to make with the person who prescribed it — LactMed itself states it is not a substitute for professional judgement.
What can I take instead of sulfamethoxazole while breastfeeding?
LactMed lists Sulfisoxazole, Trimethoprim-Sulfamethoxazole as alternate drugs to consider. That is the database's own list for this drug — whether any of them suits you depends on what you are treating.
Does sulfamethoxazole pass into breastmilk?
LactMed's measured drug levels for sulfamethoxazole are quoted in full on this page, under "How much gets into breastmilk".
Do I need to pump and dump after taking sulfamethoxazole?
LactMed does not frame its records that way — it reports measured drug levels in milk and what has been observed in breastfed infants, which is what this page quotes. "Pump and dump" advice for a specific drug and dose should come from your clinician or a pharmacist, not from a general rule.
More on sulfamethoxazole
LactMed states that the information it presents is not a substitute for professional judgement, and that you should consult your healthcare provider for breastfeeding advice related to your particular situation. Nothing on this page is medical advice.