Anne:  I currently have a patient who has had Graves' disease for a few
years, and has been on tapazole and PTU.  She is due in the next week or
so, and her endocrinologist reported that her levels of thyroid
stimulating immunoglobulin are high and therefore her baby has a good
chance of developing neonatal transient hyperthyroidism.  I researched
the issue in the literature and with the endocrinologist, and there will
be no contraindication to breastfeeding.  Both PTU (propylthiouracil) and
tapazole (methimazole) are considered compatible with breastfeeding in
the AAP paper (Pediatrics Jan 1994).
Although my patient does not require radioactive imaging studies, the AAP
paper has listings of the radioisotopes and the duration of radioactivity
in breastmilk.  I-123 stays in milk up to 36 hours, I-125 stays for 12
days, and I-131 as long as 14 days.  There was a fairly detailed
discussion of radioactive iodine, especially for therapeutic use, which
you should be able to find in the archives (approximately a month ago).
Hope this helps.  Alicia.  [log in to unmask]