transport into breastmilk
Jenny Thomas, MD, MPH, IBCLC, FAAP, FABM
Too many women are told to discard their milk because of the need
for medication. Often, this information is just plain wrong, causing unnecessary interruptions of breastfeeding, impacting milk supply and
confidence, and creating unneeded expenses.
Breastmilk is protected from blood by a a blood:milk barrier very similar to the
blood:brain barrier. In order for a
medication to cross from the bloodstream into breastmilk it has to be able to
cross that blood:milk barrier.
I have cool
slides to illustrate this. In the first few days after birth, gap
junctions (the space in between cells) are open and "leaky" allowing for
substances to easily cross into milk from the bloodstream. That is not really a
big deal since the babies are getting a very small amount of colostrum.
Any medication that mom takes is not likely to have much of an effect because
the baby is not taking in (appropriately!) a large amount of colostrum.
By about day
4 of life, those gap junctions close, meaning any medication now
would need to penetrate 2 lipid
to get into milk. After closure of the gap junctions,
medication would need to have certain characteristics or transporters to get into milk.
For example, molecules that easily get into milk need to be small and lipophilic (meaning
the molecule can interact easily with lipids). Substances like alcohol are in
this lipophilic category. Because they are lipophilic, they can go right through the blood:milk barrier, but then come right out
(illustrated the "simple diffusion" slide) . Other
molecules have specialized transporters so they can enter milk. Others,
like secretory IgA, have
a special protein transporter. I have illustrated all these ideas in the
For a drug to make a difference:
to be orally available: That means that if the baby gets the
medication from drinking breastmilk, the medication needs to work if taken
orally. Many medications don't work orally. For example,
generation cephalosporins (the last two are classes of antibiotics), and radiocontrast agents
(for MRI or CT scans) do not work if taken orally.
Often they are injections or given IV.
If you gave those medications orally, they would have little effect. So, if the
baby would get the medication by drinking breastmilk, it makes little
difference. That's not how that medication works.
needs to absorbed through the GI tract:
The medication only has an effect if it can get into the maternal bloodstream.
If it can't be absorbed from the GI tract into the bloodstream, it can not get
into milk. Examples of medications that are into absorbed from the GI tract and
can not get into the bloodstream in significant amounts are morphine and
sumatriptan (which are sequestered in the liver),
salts (used in MRIs),
contrast agents (used for CTs) and
(an antibiotic). Take note here: MRIs and CT scans can be done safely
without discarding milk.
Large molecular weight proteins like insulin and interferon can not cross
the very protective blood:milk barrier because they are too big to get
through those lipid bilayers and therefore they do not cross into breastmilk.
available to infant:
Could the baby ingest it and have it do something clinically?
If the medication is not given in a way that is meant to work by taking it
by mouth it is unlikely to have an effect on the baby. For example,
intravenous medications aren't ingested, so they make little difference. Topical
medications aren't eaten so they are considered compatible with
by infant GI tract.
Can the baby digest it?
A topical medication wouldn't be eaten, nor digested. Therefore, they don't
get into the bloodstream and make excellent medication choices if possible.
in a clinically significant amount:
When it finally makes into the
babies bloodstream, if it does, how much gets there?
medication cannot get into the bloodstream, it cannot get into the
We need to consider:
transferred to the infant: After all the considerations we have talked
about, what gets to the baby is likely to be less than what mom originally
took. An exception to that would be alcohol; the amount of alcohol in mom's
blood is exactly that in her milk. (Remember, alcohol is lipophilic, small
in size, gets into the maternal bloodstream, is orally available to the baby
and can be digested by the baby-- pretty much everything that makes a
substance able to enter breastmilk.)
age of the infant: The amount that a 10 month old, who is taking solids,
weighs double or nearly triple their birth weight, and is probably nursing less
frequently, will be very different that the amount that an infant receives.
of the medication on the baby: Some of the same side effects that mom
experiences may occur in the baby. While antibiotics are almost all
compatible with breastfeeding, the amount that crosses into milk can cause
diarrhea or yeast infections in the baby.
of the medication on maternal milk supply: Let's not forget this one! A
medication may be perfectly compatible with breastfeeding for mother and
baby but works on a hormone that makes milk. For example,
bupropion (otherwise known as Wellbutrin and Zyban)
is compatible with breastfeeding but increases dopamine. Dopamine decreases
prolactin, the hormone that makes milk. So when this medication increases
dopamine, it decreases prolactin, which can then decrease the amount of milk
Points to remember:
is important! When we do a risk:benefit analysis for the medication, we need
to consider the risks of not breastfeeding. "Just to be safe" overwhelmingly
means continuing to breastfeed.
information is out there. Anyone can access it. Sometimes synthesizing all
that information requires some help. And help is out there. Please tell me you
will find it.
better to assume that the medication is compatible (not safe) than
ask the mother to pump and discard her milk without researching the answer.
What medication can I take
while I'm breastfeeding?
We don't throw milk away without a really,
really good reason. Like you are getting chemotherapy or decided to do
Most medications are compatible (I try to
avoid saying "safe") with
If you don't really need to take it (like cold medications) don't take it.
This is the resource recommended by
the American Academy of Pediatrics. Try
it right now if you'd like. Your inquiry will go to the National
Library of Medicine page dedicated to medications in breastmilk. They also
have an app that you can download right to your phone so that you always
have access to the information you need and can share if you need to.
(I have asked mothers to download it right in my office if I know they are
having a procedure, surgery or are having medical problems. They can share
that information with their providers right on the spot.)
Infant Risk Center
- and Me, although I'm just going to check LactMed