How would a doctor treat himself if he had colitis?

He wouldn't: A doctor who treats himself for any serious malady has a fool for a patient!

Colitis: I would seek help from a reputable gastroenterologist. It would also depend on what form of colitis you (or i....Since you asked:-))had. There are many forms of colitis.

Not literally: We assume you mean what do those with the "inside knowledge" do for a specific condition. Dr ginn answered it best. Seek treatment from a competent expert in that area of medicine.

5ASA with quick : Escalation of treatment as needed. This is assuming you are speaking of uc or crohn's colitis ; and being followed by a gi.