Last weekend, I suffered a terrible bout of poison ivy while working in the yard of a new home. This is what I learned:
If you know you've been exposed to the plant immediately wash with a cleaner called Tecnu, which is specifically designed to neutralize the plant oil. Wash double wash everyting thoughly (super important). Also, make absolutely sure you wash any exposed clothing, as the oil can linger on clothing and tools, causing reinfliction.
If you do have a reaction to the plant it will take 1-2 weeks to heal untreated or several days using prescription drugs All the over the counter medication I initially tried were worthless, including cortiad, benadryl, calamine etc. Best bet is to go to the doctor as quickly as possible and get topical steriod cream (diprelene) and an oral antihistimes (Zyrtec?) For super severe cases a steriod injection may be prescribed.
Hot as you can stand showers will offer some temporary itch relief. Wrapping the affected part in banage helps to sleep to at night.
Of course the best is just to know how to recognize and avoid this vile class of plants.