Methenamine Pregnancy and Breastfeeding Warnings

Methenamine is also known as: Hiprex, Mandelamine, Urex

Methenamine Pregnancy Warnings

Methenamine has been assigned to pregnancy category C by the FDA. Animal studies have not been reported. It is known to cross the placenta. Two studies of methenamine use during pregnancy have not reported an increase adverse fetal outcome when compared to controls. Methenamine should only be given during pregnancy when benefit outweighs risk.

The Collaborative Perinatal Project reported 49 pregnancies involving first-trimester exposure to methenamine. Birth defects were reported in 4 infants. In 299 pregnancies involving exposure to methenamine anytime during pregnancy, 12 malformations were reported (5.34 expected). In a review of 229,101 deliveries to Michigan Medicaid patients, 209 first-trimester exposures to methenamine were recorded and 778 exposures anytime during pregnancy. A total of 8 birth defects were reported with first-trimester exposure (8 expected) and included (observed/expected) one cardiovascular defect, one oral clefts, one polydactyly, and one limb reduction.

Methenamine Breastfeeding Warnings

Methenamine is excreted into human milk. The manufacturer recommends that due to the potential for serious adverse reactions in nursing infants, a decision should be made to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.

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