Can lactating mothers take flagyl?

Yes: Having said that, it also depends on the dosing and the duration of treatment. The safety of Flagyl is labeled "conditional" which means depends on the dosing and the patient. Flagyl is used safely in neonates and infants so a normal dose in breast milk is fine as long as it is not an extreme dose and extreme duration.

AAP & Flagyl: Metronidazole (Flagyl) is rated by the AAP as a drug whose effect on infants is unknown, but it may be of concern because older studies found its use in pregnancy to be associated with mutagenicity. Nevertheless, the amount transferred to the infant through breast milk is much lower than the therapeutic dosage for infants, and no adverse effects have been reported from exposure through breast milk