Can you take trimethoprim while breastfeeding?
What LactMed says
The National Library of Medicine’s own summary, quoted in full. We do not write a verdict of our own on this question, and we do not compress theirs into a label.
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.
Quoted from Trimethoprim — Drugs and Lactation Database (LactMed®), National Institute of Child Health and Human Development, revised November 15, 2024.
What LactMed would consider instead
LactMed ends this record by naming the drugs it would consider in place of trimethoprim. Whether any of them fits depends on what you are treating — this is the database’s list, not a recommendation from us.
How much trimethoprim gets into breastmilk
Maternal Levels. In 20 mothers in the immediate postpartum period given oral trimethoprim, peak milk levels occurred 3 hours after the dose. In 14 of these women who received a daily dosage of 320 mg, the peak milk level averaged 2.4 mg/L and the trough averaged 1 mg/L. In 6 other women who received a daily dosage of 480 mg, the peak milk level averaged 4 mg/L and the trough averaged 1.5 mg/L. The authors calculated that a breastfed infant would receive a daily dosage of 0.75 mg with a maternal dosage of 320 mg daily and 1.7 mg with a maternal dosage of 480 mg.
Forty women in the early postpartum period received oral co-trimoxazole and had milk levels measured several times daily for 5 days. After trimethoprim doses of 320 mg daily, average milk levels were about 2 mg/L. Milk levels increased to about 3 mg/L by day 5 of therapy. In 10 other women who received trimethoprim 480 mg daily, average milk levels were only slightly higher. With the usual dose of trimethoprim 320 mg daily, an exclusively breastfed infant would be expected to receive 0.45 mg/kg daily of trimethoprim. This is very low in comparison to the established treatment dosages of 8 mg/kg daily for infants over 2 months of age.
Infant Levels. Relevant published information was not found as of the revision date.
What has been seen in breastfed infants
In one study, no adverse effects were noted in infants during 4 days of maternal therapy with co-trimoxazole.
In a telephone follow-up study, 12 nursing mothers reported taking co-trimoxazole (dosage unspecified). Two mothers reported poor feeding in their infants. Diarrhea was not reported among the exposed infants.
Effects on milk supply
Relevant published information was not found as of the revision date.
Frequently asked questions
Can you take trimethoprim while breastfeeding?
What the NIH's Drugs and Lactation Database says about Trimethoprim while breastfeeding — quoted in full. The full record is quoted on this page, and the decision is one to make with the person who prescribed it — LactMed itself states it is not a substitute for professional judgement.
What can I take instead of trimethoprim while breastfeeding?
LactMed lists Ciprofloxacin, Levofloxacin, Nitrofurantoin as alternate drugs to consider. That is the database's own list for this drug — whether any of them suits you depends on what you are treating.
Does trimethoprim pass into breastmilk?
LactMed's measured drug levels for trimethoprim are quoted in full on this page, under "How much gets into breastmilk".
Do I need to pump and dump after taking trimethoprim?
LactMed does not frame its records that way — it reports measured drug levels in milk and what has been observed in breastfed infants, which is what this page quotes. "Pump and dump" advice for a specific drug and dose should come from your clinician or a pharmacist, not from a general rule.
More on trimethoprim
LactMed states that the information it presents is not a substitute for professional judgement, and that you should consult your healthcare provider for breastfeeding advice related to your particular situation. Nothing on this page is medical advice.