Is Methenamine Mandelate safe while breastfeeding?

Summary of use during breastfeeding

Both methenamine and mandelic acid pass into milk in small quantities. Methenamine mandelate appears acceptable to use, even while nursing a newborn.

Effects on the breastfed infant

Four newborn infants were allowed to breastfeed in one study after a maternal dose of 1 gram of methenamine hippurate. No adverse effects were reported.[1]

Six infants were allowed to nurse during maternal ingestion of the large daily dosage of 12 grams of mandelic acid. There was no clinical or laboratory evidence of harm to the infants.[2]

Effects on milk supply

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

Levels in milk

Maternal Levels. Six mothers nursing newborn infants were given methenamine hippurate 1 gram orally. Five hours after the dose, a mean methenamine concentration of 7 mg/L was found in milk. In two other women, milk concentrations averaged 9.1 mg/L at 2 to 3 hours after a 1 gram dose of methenamine hippurate orally and 4.3 mg/L at 6 to 7 hours after the dose. Based on the amount of milk ingested, the authors calculated the dose the infants received to be 0.05 to 0.1 mg/kg, which is about 1% of the adult dose.[1]

Six mothers were given mandelic acid 3 grams orally 4 times daily, a dose far in excess of that contained in a typical dose of methenamine mandelate. The authors estimated that their exclusively breastfed infants received an average 273 mg of mandelic acid daily in breastmilk. This amounted to an average daily dosage of 86 mg/kg in the 6 infants, which is about 48% of the adult dosage.[2]

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

Alternatives LactMed lists

• Methenamine Hippurate