The prestigious mother risk clinic at the Hospital for Sick Children
(Toronto) counsels mothers that it is okay to breastfeed while taking
metronidazole.  In addition, the Canadian version of the PDR says this about
metronidazole:

"Metronidazole has been cited as a drug contraindicated during lactation.
This advice is based on reports that the drug is metagenic in bacteria and
carcinogenic in rodents when taken throughout their lives.  Specific
untoward effects in a nursing infant as a result of metronidazole ingestion
have not been reported.  Without more direct evidence of the harmful effects
of short term use in humans it seems overly conservative to withhold the
drug or discontinue breastfeeding..."

Hale too long to quote in full, but says "no reports of untoward effects in
breastfed infants have been published for the 2 gm stat dose, or the 250 mg
three times daily for 10 days regimen."

Jack Newman, MD, FRCPC

Jack Newman, MD, FRCPC