What are the recommended first aid measures for treating a poison ivy rash?

The recommended first aid measures for treating a poison ivy rash include washing the affected area with soap and water, applying a cold compress to reduce itching and inflammation, taking antihistamines to relieve itching, and using over-the-counter hydrocortisone cream to reduce redness and swelling. If the rash is severe or spreads to a large area, seek medical attention.