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Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-.

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Drugs and Lactation Database (LactMed) [Internet].

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Methenamine

Last Revision: January 18, 2021.

Estimated reading time: 1 minute

CASRN: 100-97-0

image 134973022 in the ncbi pubchem database

Drug Levels and Effects

Summary of Use during Lactation

Both the hippurate and mandelate salts of methenamine pass into milk in small quantities and appear 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 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]

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

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]

Effects on Lactation and Breastmilk

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

Alternate Drugs to Consider

Methenamine Hippurate, Methenamine Mandelate

References

1.
Allgén LG, Holmberg G, Persson B, et al. Biological fate of methenamine in man. Acta Obstet Gynecol Scand. 1979;58:287–93. [PubMed: 484222]

Substance Identification

Substance Name

Methenamine

CAS Registry Number

100-97-0

Drug Class

Breast Feeding

Lactation

Anti-Infective Agents, Urinary

Antibacterial Agents

Disclaimer: Information presented in this database is not meant as a substitute for professional judgment. You should consult your healthcare provider for breastfeeding advice related to your particular situation. The U.S. government does not warrant or assume any liability or responsibility for the accuracy or completeness of the information on this Site.

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