Is Trimethoprim safe while breastfeeding?

Effects on the breastfed infant

In one study, no adverse effects were noted in infants during 4 days of maternal therapy with co-trimoxazole.[ 1 ] 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.[ 4 ]

Effects on milk supply

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

Levels in milk

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.[ 1 , 2 ] 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.[ 3 ] 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.

Alternatives LactMed lists

• Ciprofloxacin
• Levofloxacin
• Nitrofurantoin