In response to Dr. Newman's comment concerning paroxetine,  there are
actually two answers or perhaps questions that have concerned me for
some time.

First,  the fact that paroxetine is rapidly displaced from the maternal
(or infant) plasma to a distal third compartment is both good and bad.
The fact that plasma levels are very small is fortunate for
breastfeeding mothers because we must all remember that the driving
force that pushes drugs into milk is the maternal plasma level.  If the
mothers plasma level of drug is small,  then the equilibrium forces that
push the drug into milk will also be very small,   hence the total
amount of medication transferred is minimal.  This is good,  and for
paroxetine,  it probably means that the total amount of drug transferred
is quite minimal,  which is what the data I previously noted seems to
indicate.

Second,  however,  if the drug is not in the plasma but distributes to a
third or peripheral compartment,  it actually may cause more suttle
problems.  In essence,  if it doesn't stay in the plasma,  it may go to
the brain's receptors and become more concentrated there (where it may
cause more problems).  Although we don't know if this is a problem with
the SSRIs(paroxetine),  I can tell you it is a problem with certain
opioid drugs such as fentanyl.  We are just now beginning to understand
that fentanyl use during delivery, rapidly equilibrates from mom to
infant (almost instantly).  However, all the current literature suggests
that "there's none in the cord blood",  which the anestheliologists use
to suggest that their meds are innocuous to the newborn, when the truth
is that fentanyl doesn't stay in the plasma,  but rapidly leaves for the
opioid receptor in the brain where it can produce neonatal sedation, and
floppy neonates.  So in this instance,  the fact that fentanyl is not
found in large concentrations in the plasma(cord blood)  simply hides
the fact that its somewhere else(brain).

So the answer to the paroxetine puzzle, and to sertraline(Zoloft ) as
well is that we must remain optimistically cautious until we know a
little more about their various comparment kinetics and concentrations.

By the way,  the paroxetine people are very interested in promoting
their product to breastfeeding mothers.   They may be interested in
funding a study of  paroxetine milk and neonatal blood levels.  We're
talking now.  So,  if any of you have breastfeeding mothers using
Paxil,  please email me directly,  I may want to enroll them in a study.


Regards
Tom Hale, Ph.D.