I got a case of PI last year that must've been for the record books. Trouble was, I kept re-infecting myself, because I had gotten the oils all over various gloves, saws, equipment, my tractor, etc. Thru the ordeal, andmy tendency to research everything beyond the point of utility (I'm a research engineer), I believe I have the ideal treatment plan:
1. Wash with Tecnu Extreme or Zanfel (I use Tecnu Extreme because it's much cheaper and just as effective) any time you've been around PI. (duh)
2. Wash with TE or Zanfel any time you see a rash starting. Wash any area that was exposed, not just where the rash is showing up. (again, duh...)
3. Go to your dermatologist or family doctor and request a 1 lb. tub of triamcinolone acetonide (synthetic corticosteroid) in petroleum jelly. Typically 0.1%.
4. Once you're absolutely sure you've succeeded in washing off all the oils, apply the steroid. Rash will be gone in 24 - 48 hours.
Most doctors seem to like prescribing prednisone for bad cases, but I do not see any good reason to take an oral steroid, when a topical is available, and generally more effective! The triamcinolone acetonide was suggested to me by a dermatologist at Penn University Hospital.