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.



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T.W. Hale, Ph.D.
Associate Professor of Pediatrics
Texas Tech University School of Medicine

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