Methenamine Mandelate

Drug Levels and Effects:

Summary of Use during Lactation:

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

Drug Levels:

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 2 to 3 hours after a 1 gram dose of methenamine hippurate orally and 4.3 mg/L 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 mandelicacid3 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 mandelicaciddaily in breastmilk. This amounted to an average dose of 86 mg/kg/day in the 6 infants which is about 48% of the adult dosage.[2]

Infant Levels.

Six mothers were given mandelicacid3 grams orally 4 times daily. Mandelicacidwas measurable in their breastfed infants' urine.[2]

Effects in Breastfed Infants:

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 dose of 12 grams daily of mandelicacid. There was no clinical or laboratory evidence of harm to the infants.[2]

Possible Effects on Lactation:

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

Alternate Drugs to Consider:

Methenamine Hippurate


1. Allgen LG, Holmberg G, Persson B et al. Biological fate of methenamine in man. Acta Obstet Gynecol Scand. 1979;58:287-93. PMID:484222
2. Berger H. Excretion of mandelicacidin breast milk. Am J Dis Child. 1941;61:256-61.

Substance Identification:

Substance Name:

Methenamine Mandelate

CAS Registry Number:


Drug Class:

  • Antiinfective Agents, Urinary

  • Antibacterial Agents

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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