To Jeffrey Fouche: There are a number of references to the use of propylthiouracil(PTU) in breastfeeding moms. I would suggest you get a copy of : Cooper DS Antithyroid drugs: to breastfeed or not to breastfeed. Am. J. Obstet. Gynecol 157:234, 1987 Kampmann JP et.al. Propylthiouracil in human milk. Lancet 1:736, 1980. In general, PTU penetrates milk very poorly and milk levels have been repeatedly documented to be minimal and clinically insignificant for the breastfeeding infant. Regardless, the ultimate test to see if the PTU is affecting the infant is to simply draw a blood sample and test the infants TSH and T4. This is very simple to do, and could be repeated ocassionally just to put people's(the doctor's) mind at ease. As to Radioactive Iodine. I-131 is the preferred drug. Iodine preferentially binds to the thyroid tissue(90%)... actually there are strong pumping mechanisms that selectively extract the iodine from blood and place it in the thyroid parenchyma( Thyroid:plasma ratio is 30:1). If radioactive iodine-131 is placed in the plasma compartment, it is almost exclusively transported into the thyroid gland. I-131 is radioactive, and emitts both a Gamma particle, and a beta particle. It is actually the beta particle that produces oxidative damage to the thyroid tissue and destroys this tissue. But nevertheless, radioactive T4, and even some radioactive iodine are still present in other tissues, and are secreted into human milk in relatively high levels. There are two decay processes involved in this process. First, I-131 as a radioactive substance decays with a half-life of 8.1 days. That means that if this product were placed in a bottle, its radioactive emissions would be 97% gone in 5 half-lives(40 days). However, in the human being, we have another process, biological half-life. This means how long does it stay in the human being(some of it being excreted via the urine). When you put these two together, the absolute biologic half-life of Iodine is somewhere less than 8.1 days, but we don't know for sure what it is. Some authors suggest that most is secreted in 14 days... other well designed studies suggest that mothers should not breastfeed for up to 50 days. Who's to know for sure. Because the infants' thyroid is critically important, I would suggest that the physician attempt to use PTU to control the Graves disease for as long as seems reasonable to the mom and the physician. If it is not working, then I-131 ablation is generally recommended. I would opt to discontinue breastfeeding permanently after I-131 treatment, just to be very safe. *********************************** T.W. Hale, Ph.D. Associate Professor of Pediatrics Texas Tech University School of Medicine ***********************************