Is Sulfamethoxazole safe while breastfeeding?
Here is what LactMed, the Drugs and Lactation Database published by the U.S. National Institute of Child Health and Human Development (NICHD), reports about Sulfamethoxazole. The text below is quoted from that source — it is not our own verdict.
Summary of use during breastfeeding
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.[1] 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.[2]
Effects on the breastfed infant
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.[4]
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.[5]
Effects on milk supply
Relevant published information was not found as of the revision date.
Levels in milk
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.[3] 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.
Alternatives LactMed lists
Source: Drugs and Lactation Database (LactMed), National Institute of Child Health and Human Development (NICHD), via NCBI Bookshelf, record “Sulfamethoxazole” (LM418). LactMed on NCBI Bookshelf. LactMed is a registered trademark of the U.S. Department of Health and Human Services.
Educational summary of an authoritative source — not medical advice. Never start, stop, or change a medicine while breastfeeding without confirming with your doctor.