Do you know what I should ask for? I have had 3 birds go down or show symptoms in the past 3 weeks.
I used valacyclovir (brand name Valtrex) whereas others have used acyclovir. I believe they are both generic and inexpensive. You have to guess on the dosage.
I have never had any problems with it, even when dosing tiny bantams, but I typically have only give the birds 1 or 2 doses (not long term). I believe kidney damage is a possible side effect. Of course there are NO studies of its use on chickens to my knowledge (there is no market for it in chickens so no one will spend the cash to study it).
Here is a thread that may interest you, a poster described how he used the drug to cure a fatal herpes virus in his birds: https://www.backyardchickens.com/threads/cure-for-herpes-virus-in-turkey’s.1405326/#post-23067015