If you ask the average physician (pedi and pharmacy included) about drugs and breastfeeding, remember that they will just tell you what the drug company tells them. They will simply reiterate what the drug says and ALL DRUGS (including Tylenol) will cover their butts and say "ask your doctor about breastfeeding" or "do not breastfeed on this drug." Sooo:
Go to the pros: The best, most respected source of medication and lactation comes from the University of Texas and a Dr. Thomas Hale, Ph.D
He studies how medications pass through a mother's milk. You can always read his forum here (login as guest): http://neonatal.ttuhsc.edu/lact/medicationforumspage.html
I have his most recent book (13th ed of Medications and Mother's Milk). I looked up Atarax for you: It is listed as an L1 (safest possible for breastfeeding - yay!). Here are the details:
No reports of any pediatric concerns. It has a half life of 3 to 7 hours (excellent - shorter the better) and reaches it's peak concentration in your blood plasma at 2 hrs after you take the drug. The drug is listed as extremely safe, but if you want to really feel good about it, simply avoid nursing around that 2 hr peak (so if you take a pill at 2pm, your peak concentration in your blood would be at 4pm. Nurse happily until about 3:30 and then wait till 4:30 to nurse again).
EDIT:
I should add that Hale's books, unlike many others, look at numerous factors: protein binding capacity of the drug, molecular weight, half lives, plasma infusion rations, etc. These are all things that pharmacies and drug companies do not look at. A drug with a high molecular weight and a high protein binding capacity has an extremely difficult time passing through breastmilk (i.e. through the the mammary epithelium).
Here is a great explanation of these terms and how they apply to the nursing mom: http://www.drjaygordon.com/development/bf/lactationrisk.asp
Sorry if this is an over-abundance of info!
Peace-Love-Boobies
K. (I run the 80 member Cape Cod Breastfeeding Moms Group - join us on FACEBOOK!)