Dear Lactnetters,

I'm mostly a lurker these days, but a question came up from a LLL help form
that I need some clarification on.  I hope you can help me.  A mom asked
about CATscans and breastfeeding; the specific tracing agent would be
renographin.  My AAPL has obtained information about this agent for me that
is confusing to me.  The information comes from the USP DI 1996, DRUG
INFORMATION FOR THE HEALTH CARE PROFESSIONAL.  One part of the info gives the
molecular weight of the agents as follows:  "RENOGRAPHIN is a Diatrizoate, an
ionic radiopaque contrast agent.  Renographin is listed  as Renographin-60
and Renographin-76.  The molecular weight of Diatrizoate meglumine is 809.13.
 Diatrizoate sodium is 635.90."   She then quotes Riordan and Auerbach: The
lower the drug's molecular weight, the more easily it passes through to milk
and vice versa.  Drugs with a high (over 200) molecular weight are restricted
from passing into human milk.  Because of their high molecular weight, they
are also not absorbed in the gastrointestinal tract.  OK so far.  Where I get
confused is the further info from the USP: "Precautions to Consider while
Breastfeeding.  Although problems in humans have not been documented, since
diatrizoates are distributed unchanged into breast milk, temporary
discontinuation of breastfeeding is recommended for at least 24 hours
following their administration."

Huh?  The molecular weight appears to me to prohibit passage into milk.  So
why/how are the molecules appearing unchanged in breastmilk?  Am I
misinterpreting this information?  I would like to be able to clarify for the
mom this apparent conflict, or if it isn't a conflict, to be able to explain
that as well.  As an LLL Leader, I can't offer any recommendations, but I
would like to offer clear information!  Thanks for any light you can shed on
this for me.

Ann Davis, LLLL, Dayton, Ohio USA
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