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Sulfamethoxazole use while Breastfeeding

Medically reviewed by Last updated on Jun 24, 2023.

Drugs containing Sulfamethoxazole: Bactrim, Bactrim DS, Septra, SMZ-TMP DS, Cotrim, Co-trimoxazole, Septra DS, Bactrim Pediatric, Sulfatrim, Bactrim IV, Show all 20 »Sulfatrim Pediatric, Gantanol, Cotrim DS, Azo Gantanol, Bethaprim, Uroplus, Uroplus DS, Septra IV, Bethaprim Pediatric, Cotrim Pediatric

Sulfamethoxazole Levels and Effects while Breastfeeding

Summary of Use during Lactation

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]

Drug Levels

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.

Effects 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.[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 Lactation and Breastmilk

Relevant published information was not found as of the revision date.

Alternate Drugs to Consider

Sulfisoxazole, Trimethoprim-Sulfamethoxazole


Zao J, Koren G, Bozzo P. Using nitrofurantoin while breastfeeding a newborn. Can Fam Physician. 2014;60:539-40. [PMC free article: PMC4055319] [PubMed: 24925943]
Chung AM, Reed MD, Blumer JL. Antibiotics and breast-feeding: a critical review of the literature. Paediatr Drugs. 2002;4:817-37. [PubMed: 12431134]
Miller RD, Salter AJ. The passage of trimethoprim/sulfamethoxazole into breast milk and its significance. In: Daikos CK, ed. Progress in Chemotherapy. Antibacterial chemotherapy. 1974;1:687-91.
Forna F, McConnell M, Kitabire FN et al. Systematic review of the safety of trimethoprim-sulfamethoxazole for prophylaxis in HIV-infected pregnant women: implications for resource-limited settings. AIDS Rev. 2006;8:24-36. [PubMed: 16736949]
Ito S, Blajchman A, Stephenson M et al. Prospective follow-up of adverse reactions in breast-fed infants exposed to maternal medication. Am J Obstet Gynecol. 1993;168:1393-9. [PubMed: 8498418]

Substance Identification

Substance Name


CAS Registry Number


Drug Class

  • Breast Feeding
  • Lactation
  • Anti-Infective Agents
  • Antibacterial Agents
  • Sulfonamides

Disclaimer: Information presented in this database is not meant as a substitute for professional judgment. You should consult your healthcare provider for breastfeeding advice related to your particular situation. The U.S. government does not warrant or assume any liability or responsibility for the accuracy or completeness of the information on this Site.

Further information

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