Maybe you can tell her that not everyone agrees that metronidazole is
contraindicated during breastfeeding. Here is a quote from the
Compendium of Pharmaceutical Specialities (Canadian PDR).
"Metronidazole has been cited as a drug contraindicated during
lactation. This advice is based on reports that the drug is mutagenic
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 in
patients with symptomatic parasitic infections for which metronidazole
may be the treatment of choice."
The baby's fussiness is not necessarily due to the drug.
Jack Newman, MD, FRCPC