>OK... I get this, Diane... but is the alcohol level in the mother's
>breastmilk the same as the alcohol level in the mother's BLOOD? That is
>what I'm struggling with here. I don't see how it canNOT be.
Okay, fine. I'll display my ignorance.
Hale's book has a nice summary at the front about various drug properties and how they affect the milk:plasma ratio.
If milk level and blood level are the same, the ratio is 1:1, and he says it is for ethanol (alcohol). But if the drug molecule is huge, it can't squeeze through the cell walls into the milk, so it doesn't appear in the milk *at all*, and the milk:plasma ratio would be 0:1. Heparin is like that. If the molecule isn't quite so huge, *some* squeezes through. So the smaller the molecule, the more the ratio creeps back up to 1:1.
But if the drug likes to stick to protein (protein-binding), it's more likely to hang onto the blood itself and not get squinched off into the alveolar cells. So the better the protein binding, the lower the milk:plasma ratio will be.
But if the drug mixes well with fats (is lipid-soluble), it can ride through the cell membranes along with the fat molecules, and raise the milk:plasma ratio.
And so on. I'm no chemist or pharmacist, so I just rely on Hale's notes at the front of his book to explain to me - yet again - what his various codes mean. The molecular weight, fat solubility, and protein-binding make sense to me, and I can see why those might affect how well drugs get into the milk. I take some of the other issues on faith :-)
Ooh, one other part that makes sense to me: If a drug is injected into the mom because it doesn't work orally (has low oral bioavailability), it makes sense that it won't work in the baby very well when *he* swallows it, either. So injected meds are less likely to be a problem.
As to half-life: After one half-life, 100 units of the drug in milk or blood have dropped to 50. After another half-life, it's down to 25. After another it's 12.5. After another it's 6.25. And after a fifth half-life it's only 3.1. In other words, after 5 half-lives, about 97 percent of the drug is gone - all of it, for practical purposes. Drug levels rise and fall in the milk and blood together; the breasts aren't cisterns that hold drug-laden milk until it's disposed of. The old "pump and dump" recommendation was just to keep the mom's supply up, not to get rid of "bad milk."
It's not really clear to me how some drugs can concentrate in milk, but some do. Even so, the amount ingested by the baby is still so small that it's not usually an issue. Especially when you consider the alternative.
I like Chris Mulford's analogy: If formula is Philadelphia and breastmilk is Hawaii, then new improved formula is... Pittsburgh. And I usually add that donor milk, or wrong-aged milk, or milk after you've taken most meds is... a few miles off Waikiki Beach :-)
Diane Wiessinger, MS, IBCLC Ithaca, NY USA
www.wiessinger.baka.com
***********************************************
To temporarily stop your subscription: set lactnet nomail
To start it again: set lactnet mail (or digest)
To unsubscribe: unsubscribe lactnet
All commands go to [log in to unmask]
The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(R)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html
|
