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Subject:
From:
Jack Newman <[log in to unmask]>
Reply To:
Lactation Information and Discussion <[log in to unmask]>
Date:
Fri, 30 May 1997 09:26:42 -0500
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If you all do not mind my musings.  In thinking about this question of
drugs in pregnancy and drugs in breastfeeding, it occurred to me that
most health professionals and lay people as well think of the breast as
a sort of placenta.  This may be their big hangup in trying to
understand why a drug may be acceptable during breastfeeding even if it
is not during pregnancy.

When a fetus is in utero, any drug the mother takes will usually (though
not always) be also distributed to the baby, usually so that the fetus'
blood level would be similar or close to that of the mother's.  This is
generally so, though there are exceptions, such as prednisone, which
apparently does *not* pass the placental barrier.  In other words, then,
if the mother is taking 500 mg three times a day of amoxycillin, in a
sense it is as if the baby were taking 500 mg three times a day, or a
similar quantity (proportional to its weight) which would give him a
blood level similar to the mother's blood level.  As Dr. Hale mentioned,
the mother will handle the drug for the baby, and accumulation is not a
concern.

However, when the baby gets the drug in the milk, he is not getting it
as if through the placenta.  He is getting only small amounts depending
on the milk:plasma ratio.  He is not getting 500 mg of amoxycillin three
times a day, he is getting perhaps (guessing here), 15 mg over 24 hours.
This does not prevent sensitization, though sensitization is uncommon in
young babies, but it certainly causes less concern about accumulation.
(This does not mean that no drugs are of concern--benzodiazepines in
neonates, for example, may accumulate quite rapidly because the half
life in the baby is very long.  This becomes less of an issue when the
baby is over a month).

Perhaps if we helped health professionals understand that the breast is
not comparable to the placenta, we will get our message across.

Jack Newman, MD, FRCPC

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