In the first place, even at the full dose, the mother did not need to
stop breastfeeding because of Flagyl.  Here is what the Compendium of
Pharmaceutical Specialities (Canadian PDR) says about metronidazole.
"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 seem
overly conservative to withhold the drug or discontinue breastfeeidng in
patients..for whom metronidazole may be the treatment of choice."

As far as asacol is concerned, the active ingredient is mesalamine
(5-aminosalicyclic acid).  The information I have is that "mesalamine is
minimally absorbed".  Also "the absorbed mesalamine is rapidly
acetylated through the gut mucosal wall and by the liver".  Thus, little
is absorbed and most of which is absorbed is rapidly metabolised.  If
any gets to the milk, very little of that is absorbed and then most of
what is absorbed is rapidly metabolised.

It seems to me that there should be no concern.

Jack Newman MD, FRCPC