Last update Jan. 29, 2022

Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ)


Safe substance and/or breastfeeding is the best option.

Mixture of 5 parts of Sulfamethoxazole and 1 part of Trimethoprim. Oral administration in two daily doses.

TRIMETHOPRIM (TMP) is excreted in breast milk in clinically non-significant amount (Borderon 1975, Miller 1974 y 1973, Arnauld 1972). No problems have been observed in infants whose mothers were treated (Ito 1993). Medication which is used in infants from the second month of age.

SULFAMETHOXAZOLE (SMX) is excreted in non-significant levels into breast milk (Miller 1974 y 1973). No adverse effects have been shown in breastfed infants (Ito 1993). Caution with those neonates suffering of hyperbilirrubinemia or Glucose-6-phosphate dehydrogenase (G6PD) deficiency is required. Avoid use in affected patients Check-up for infant jaundice.

Although rare, the possibility of transient gastroenteritis due to alteration of the intestinal flora in infants whose mothers take antibacterial should be taken into account.(Ito 1993)

Expert authors consider the use of TMP-SMX to be compatible during breastfeeding. (Hale, LactMed, Schaefer2015, Mitrano 2009, Kaiser 2007, Chin 2001)

The American Academy of Pediatric states that TMP-SMX is usually compatible with breastfeeding medication. (AAP 2001)

WHO List of Essential Medicines from 2002 has classified TMP as compatible with breastfeeding and  SMX as compatible with breastfeeding for older, healthy full- term infants. Avoid if possible if the infant is premature or less than 1 month old. Monitor the infant for side- effects (haemolysis and jaundice). Avoid in infant with G6PD deficiency. (OMS-UNICEF 2002)

See below the information of these related products:


We do not have alternatives for Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) since it is relatively safe.

Suggestions made at e-lactancia are done by APILAM team of health professionals, and are based on updated scientific publications. It is not intended to replace the relationship you have with your doctor but to compound it. The pharmaceutical industry contraindicates breastfeeding, mistakenly and without scientific reasons, in most of the drug data sheets.

Jose Maria Paricio, Founder & President of APILAM/e-Lactancia

Your contribution is essential for this service to continue to exist. We need the generosity of people like you who believe in the benefits of breastfeeding.

Thank you for helping to protect and promote breastfeeding.

José María Paricio, founder of e-lactancia.

Other names

Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) is also known as

Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) in other languages or writings:


Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) belongs to these groups or families:


Main tradenames from several countries containing Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) in its composition:

  • Abactrim™. Contains other elements than Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) in its composition
  • Bactrim™. Contains other elements than Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) in its composition
  • Cotrim™. Contains other elements than Trimethoprim-Sulfamethoxazole (TMP-SMX; TMP-SMZ) in its composition
  • Septrin


Variable Value Unit
Oral Bioavail. 85 - 100 %
Molecular weight T/S: 290 / 253 daltons
Protein Binding T/S: 45 / 70 %
VD T: 7.4 / 0.19 l/Kg
pKa T/S: 17.3 / 6.16 -
Tmax 1 - 4 hours
6 - 12 hours
M/P ratio T/S: 1.3 /0.06 -
Theoretical Dose T/S: 0.3-0.8 / 0.8 mg/Kg/d
Relative Dose T/S: 6-10 / 1.2-5 %
Ped.Relat.Dose T/S: 4-10 / 1.2 - 2.5 %


  1. Hale TW. Medications & Mothers' Milk. 1991- . Springer Publishing Company. Available from Consulted on April 10, 2024 Full text (link to original source)
  2. Schaefer C, Peters P, Miller RK. Drugs During Pregnancy and Lactation. Treatment options and risk assessment. Elsevier, Third Edition. 2015
  3. Amir LH. y el Comité de protocolos de la Academy of Breastfeeding Medicine. Protocolo clínico de la ABM n.o 4: Mastitis, modi cado en marzo de 2014. Breastfeed Med. 2014;9(5):239-243. Abstract Full text (link to original source) Full text (in our servers)
  4. Butler DC, Heller MM, Murase JE. Safety of dermatologic medications in pregnancy and lactation: Part II. Lactation. J Am Acad Dermatol. 2014 Mar;70(3):417.e1-10; quiz 427. Abstract
  5. Amir LH; Academy of Breastfeeding Medicine Protocol Committee. ABM Clinical Protocol #4: Mastitis, Revised March 2014. Breastfeed Med. 2014;9(5):239-243. Abstract Full text (link to original source) Full text (in our servers)
  6. Amir LH, Pirotta MV, Raval M. Breastfeeding--evidence based guidelines for the use of medicines. Aust Fam Physician. 2011 Sep;40(9):684-90. Review. Abstract Full text (link to original source) Full text (in our servers)
  7. Chen LH, Zeind C, Mackell S, LaPointe T, Mutsch M, Wilson ME. Breastfeeding travelers: precautions and recommendations. J Travel Med. 2010 Jan-Feb;17(1):32-47. Abstract Full text (link to original source) Full text (in our servers)
  8. Mitrano JA, Spooner LM, Belliveau P. Excretion of antimicrobials used to treat methicillin-resistant Staphylococcus aureus infections during lactation: safety in breastfeeding infants. Pharmacotherapy. 2009 Sep;29(9):1103-9. Abstract
  9. Spencer JP. Management of mastitis in breastfeeding women. Am Fam Physician. 2008 Abstract Full text (link to original source) Full text (in our servers)
  10. Kaiser J, McPherson V, Kaufman L, Huber T. Clinical inquiries. Which UTI therapies are safe and effective during breastfeeding? J Fam Pract. 2007 Abstract Full text (link to original source)
  11. Forna F, McConnell M, Kitabire FN, Homsy J, Brooks JT, Mermin J, Weidle PJ. Systematic review of the safety of trimethoprim-sulfamethoxazole for prophylaxis in HIV-infected pregnant women: implications for resource-limited settings. AIDS Rev. 2006 Abstract
  12. Mahadevan U, Kane S. American gastroenterological association institute technical review on the use of gastrointestinal medications in pregnancy. Gastroenterology. 2006 Jul;131(1):283-311. Review. Abstract Full text (link to original source) Full text (in our servers)
  13. WHO / UNICEF. BREASTFEEDING AND MATERNAL MEDICATION Recommendations for Drugs in the Eleventh WHO Model List of Essential Drugs. Department of Child and Adolescent Health and Development (WHO/UNICEF) 2002 Abstract Full text (link to original source) Full text (in our servers)
  14. AAP - American Academy of Pediatrics Committee on Drugs. Transfer of drugs and other chemicals into human milk. Pediatrics. 2001 Sep;108(3):776-89. Abstract Full text (link to original source) Full text (in our servers)
  15. Chin KG, McPherson CE 3rd, Hoffman M, Kuchta A, Mactal-Haaf C. Use of anti-infective agents during lactation: Part 2--Aminoglycosides, macrolides, quinolones, sulfonamides, trimethoprim, tetracyclines, chloramphenicol, clindamycin, and metronidazole. J Hum Lact. 2001 Feb;17(1):54-65. Abstract
  16. Ito S, Blajchman A, Stephenson M, Eliopoulos C, Koren G. Prospective follow-up of adverse reactions in breast-fed infants exposed to maternal medication. Am J Obstet Gynecol. 1993 May;168(5):1393-9. Abstract
  17. Fulton B, Moore LL. Antiinfectives in breastmilk. Part II: Sulfonamides, tetracyclines, macrolides, aminoglycosides and antimalarials. J Hum Lact. 1992 Dec;8(4):221-3. Review. No abstract available. Abstract
  18. Borderon E, Soutoul JH, Borderon JC. Excrétion des antibiotiques dans le lait humain. [Excretion of antibiotics in human milk]. Med Mal Infect. 1975;5:373-6.
  19. Miller RD, Salter AJ. \ The passage of trimethoprim/sulpha-methoxazole into breast milk and its significance. \ Proceedings of the Eighth International Congress of Chemotherapy, Athens. Hellenic Society for Chemotherapy, 1974:687-91. (cit. Briggs 2015) 1974
  20. Miller RD, Salter AJ. The passage of trimethoprim/sul­ famethoxazole into breast milk and its significance. In Daikos GK(ed): Proceedings of the 8th Congress of Chemotherapy, Athens, 1973, Hellenic Society, Athens,1973, p 687-691. (cit. Hale) 1973
  21. Arnauld R, Soutoul JH, Gallier J, Borderon JC, Borderon E. Etude du passage de la trimethprim dans le lait maternel. [A study of the passage of trimethoprim into the maternal milk]. [Study on the passage of trimethoprin into mother's milk]. Ouest Med. 1972;25:959-64. (Cit. Briggs 2015). 1972

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