The Basics
What is Trimethoprim?
Used to treat urinary tract infections (UTIs), such as cystitis.
Brand names for Trimethoprim
Trimethoprim
How Trimethoprim is classified
Anti-Infective Agents – Urinary, Antibacterial Agents, Folic Acid Antagonists
Trimethoprim During Pregnancy
Trimethoprim pregnancy category
Category CNote that the FDA has deprecated the use of pregnancy categories, so for some medications, this information isn’t available. We still think it’s useful to list historical info, however, given what a common proxy this has been in the past.
What we know about taking Trimethoprim while pregnant
Trimethoprim (trimethoprim (trimethoprim tablet) tablet) has been shown to be teratogenic in the rat when given in doses 40 times the human dose. In some rabbit studies, the overall increase in fetal loss (dead and resorbed and malformed conceptuses) was associated with doses six times the human therapeutic dose. While there are no large, well-controlled studies on the use of trimethoprim (trimethoprim (trimethoprim tablet) tablet) in pregnant women, Brumfitt and Pursell,3 in a retrospective study, reported the outcome of 186 pregnancies during which the mother received either placebo or trimethoprim (trimethoprim (trimethoprim tablet) tablet) in combination with sulfamethoxazole. The incidence of congenital abnormalities was 4.5% (3 of 66) in those who received placebo and 3.3% (4 of 120) in those receiving trimethoprim (trimethoprim (trimethoprim tablet) tablet) and sulfamethoxazole. There were no abnormalities in the 10 children whose mothers received the drug during the first trimester. In a separate survey, Brumfitt and Pursell also found no congenital abnormalities in 35 children whose mothers had received trimethoprim (trimethoprim (trimethoprim tablet) tablet) and sulfamethoxazole at the time of conception or shortly thereafter. Because trimethoprim may interfere with folic acid metabolism, trimethoprim (trimethoprim (trimethoprim tablet) tablet) should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus
Taking Trimethoprim While Breastfeeding
What are recommendations for lactation if you're taking Trimethoprim?
Because of the low levels of trimethoprim in breastmilk, amounts ingested by the infant are small and would not be expected to cause any adverse effects in breastfed infants.
Maternal / infant drug levels
Because of the low levels of trimethoprim in breastmilk, amounts ingested by the infant are small and would not be expected to cause any adverse effects in breastfed infants.
Possible effects of Trimethoprim on milk supply
Relevant published information was not found as of the revision date.
Possible alternatives to Trimethoprim
Ciprofloxacin, Levofloxacin, Nitrofurantoin.
List of References
Lactation sources: Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK501922/1. Arnauld R, Soutoul JH et al. [Study on the passage of trimethoprim into mother’s milk]. Ouest Med. 1972;25:959-64.
2. Borderon E, Soutoul JH et al. [Excretion of antibiotics in human milk]. Med Mal Infect. 1975;5:373-6.
3. 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.
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
Disclaimer: This material is provided for educational purposes only and is not intended for medical advice, diagnosis, or treatment. Consult your healthcare provider with any questions.
