This is a difficult one.  Like all medications, some will get into the
milk.  It is metabolized to mercaptopurine which is also a quite toxic
drug.  Since the half lives of these drugs are short (probably less
than an hour) the physician might be able to find a dosing schedule
which will allow nursing.  For example sometimes azathioprine is used
as a single dosage once daily.  If the baby sleeps a long time at
night, it might be possible to give the azathioprine after the last
feeding. Perhaps the first morning feeding (if the baby sleeps through
the night), could be given as previously (before azathioprine)
expressed milk.  Maybe it could be possible to look at treating the
mother with prednisone alone, rather than both, at least until the
baby does sleep through, or until the baby is old enough that he will
eat solids enough that he does not need to nurse during the day, and
then the azathioprine can be given in the morning, after the first
nursing.  Maybe interferon could be tried, if it is a possibility in
her case.

Jack Newman, MD, FRCPC