K.P.
I am *so* glad this doctor is encouraging her to continue breastfeeding even while taking medication -- most docs will "err on the side of caution" [ha!] and recommend that mothers stop breastfeeding at the drop of a hat, so this is refreshing to hear.
Most medications do not enter breastmilk in large enough quantities to have a clinical effect in the baby [http://www.mothering.com/breastfeeding/breastfeeding-and-.... From the American Academy of Pediatrics [http://pediatrics.aappublications.org/content/108/3/776.f...] - both of those drugs are listed as having "no effect" on breastfeeding or on the baby.
Here's a simple version of what is happening: the mother takes the drug, and some of it enters the bloodstream; some of what is in her bloodstream is used by her body to create breastmilk. So, the baby gets a very reduced percentage of a percentage of the original drug.
You can also check out the KellyMom website for a fantabulous resource on breastfeeding [http://kellymom.com/health/index.html].