Yup Zanfel is as good as it gets to deal with poison when ya get it.
We too have loads of sumac here and I hear some folks are allergic to it but I'm not, never have been. Now poison oak, poison ivy or cowitch will break me out if I just walk by within 10' of it. OK maybe it really has to touch me.
But in spite of that sumac has never bothered me. I do have a daughter in law who is allergic.
I used a product called Ivy Rest last time I got infected and it seemed to work almost as good as Zanfel.