Drug Levels and Effects:

Summary of Use during Lactation:

With healthy, full-term infants it appears acceptable to use sulfamethoxazole during breastfeeding after the newborn period. 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.Sulfamethoxazoleshould be avoided while breastfeeding a G6PD-deficient infant.[1]

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.[2] 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.[3]

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 andtrimethoprimduring breastfeeding (time postpartum and dosage not reported), none reported diarrhea, drowsiness or irritability in her infant. Two mothers reported poor feeding in their infants.[4]

Possible Effects on Lactation:

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

Alternate Drugs to Consider:



1. Chung AM, Reed MD, Blumer JL. Antibiotics and breast-feeding: a critical review of the literature. Paediatr Drugs. 2002;4:817-37. PMID:12431134
2. Miller RD, Salter AJ. The passage oftrimethoprim/ sulfamethoxazole into breast milk and its significance. In: Daikos CK, ed. Progress in Chemotherapy. Antibacterial chemotherapy. 1974;1:687-91.
3. Forna F, McConnell M, Kitabire FN et al. Systematic review of the safety oftrimethoprim- sulfamethoxazole for prophylaxis in HIV-infected pregnant women: implications for resource-limited settings. AIDS Rev. 2006;8:24-36. PMID:16736949
4. 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. PMID:8498418

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Antiinfective Agents

  • Antibacterial Agents

  • Sulfonamides

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

    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.