Maybe behind on this thread, but I had a client a while ago on
phenobarbitol who had a sympathetic doc who worked out for her when she
could safely feed (giving time for the drug not to appear in the breast
milk). As far as I remember she managed to fully bf - obviously the baby
was very co-operative in going a convenient (and longish) time between
feeds right from the start.  Baby thrived, though.

Heather Welford Neil
NCT bfc Newacstle upon Tyne UK