What's the best treatment to get rid of pityriasis rosea?

Nothing.: If you're sure it's pityriasis rosea, you don't need to do anything; it will go away on its own. However, dermatologists often order a blood test to be sure it is not a similar-appearing but more serious disease, which does need treatment. So if you're not sure, or if the rash doesn't go away within a reasonable period of time, see a dermatologist.

Resolves with time: Pityriasis rosea is usually self-limited, clearly in most cases in 6-8 weeks. There is no treatment that speeds clearance. However medicines may be prescribed to reduce itching in those who have significant itching. You can find more information at http://www.Aad.Org/skin-conditions/dermatology-a-to-z/pityriasis-rosea/diagnosis-treatment/pityriasis-rosea-diagnosis-treatment-and-outcome.