This question has been up several times on lactnet.  There should be no
problem breastfeeding and the mother taking Asacol.  There is no need
for her to take half dosage unless she is getting good relief of
symptoms with half dosage.

From the Compendium of Pharmaceutical Specialities (Canadian PDR):

"Once released in the colon, mesalamine (the active ingredient) is
minimally absorbed...Aproximately 20% of the administered dose released
in the colon is absorbed, with about 80% excreted in the feces.  The
absorbed mesalamine is rapidly acetylated through the gut mucosal wall
and by the liver".

In other words, the baby won't get any.  By the way, is the pediatrician
aware of the possible protective effect of breastfeeding in preventing
inflammatory bowel disease?  Or is that just theory for him/her?  The
mother should know this when making any sort of decision.

Jack Newman, MD, FRCPC