I also have a long history of crazy sensitivity to poison ivy and can confirm that most topical solutions are useless for me, but the ones that break up and dry the oil are the best you can do without steroids.
For decades I've just gone straight to the steroids which are far, far faster than anything else--but they don't give them out easily unless it's a bad problem. Pills usually, a shot if it's really bad (in your system, as David notes).
Worst I've ever seen for myself and hordes of people happened on Martha's Vineyard in the late 80s. The Wampanoag tribe that resides in Gay Head (now called Aquinnah) held a music festival in a large field overlooking the cliffs and ocean, and they needed to clear the field for the concert area. Did you know that Native Americans don't get poison ivy? They cleared an entire field full of it, reducing it to what looked like grass clippings. Except it wasn't grass--it was poison ivy. The entire field. So everyone laid their blankets, chairs and bodies on a field full of micro-particles of poison ivy. The Martha's Vineyard Hospital had an emergency room full of poison ivy patients for days. I knew it was going to be real trouble for me and demanded the steroid shot. I think that was the last time I had the shot; everything since has obviously been less traumatic, so I've gotten the pills. Mostly I just stay as far away as possible. If I think I have come into contact I either remove and wash all my clothes and shower immediately if I am close enough to home; or I dive in the ocean and scrub the hell out of the affected area.
Good luck.
