Re: Imitrex(Sumatriptan)

        Sumatriptan is a blocker of 5-HT (Serotonin) receptors.  It is
marketed solely for the treatment of migraine headache.  It is not an
analgesic, rather it produces a rapid vasoconstriction in various regions
of the brain, thus reducing the cause of migraines.

        The only data available is from the pharmaceutical company.  It is
available in oral tablets and an injectible for subcutaneous injection.
The plasma half-life is rather short ( about 2.5 hrs).  It has a high
volume of distribution,  which means that the drug rapidly enters the
bloodstream and then exits to other periheral compartments.  Therefore, the
plasma level is somewhat small.

        In studies with rodents(rats),  the milk:plasma ratios are quite
high, from about 6.3 at 1 hour  to 7.8 at 4 hours(IV injection).
Sumatriptan is apparently ion trapped in in milk.   At 24 hours the drug is
undetectible in milk and plasma.   However,  although the M:P ratio is
high,  the actual amount of drug present in milk was quite small, 268 ng/ml
at one hour, 114 ng/ml at 1.2 hrs,   thus suggesting that the large volume
of distribution of this drug sequesters most of it in peripheral
compartments, not the plasma compartment which feeds the milk compartment.
Another good piece of info is that the oral bioavailability of this product
is poor,  averaging only 15%.  Hence infant absorption would be greatly
limited.  The oral dose in adults is 25 mg.  An infant would have to drink
94 liters of milk per day, to get an adult dose of 25 mg(assuming this rat
data is close to human data).

        As we know, the side effects are minimal, and include tingling, and
hot sensations.  The pharmaceutical company routinely recommends a 24
cessation of breastfeeding after taking the medication.  We do not have any
pediatric data concerning kinetics, absorption, etc.


Tom Hale