Humira brings in 8 bil annually. But since Humiras approval in 2002, the company (Abbott) has been continuosly investing in phase 3 studies to expand its usage label. Humira is FDA approved for multiple indications supported by their ongoing studies - the most recent of which is their fall 2012 approval for ulcerative colitis. Prurisol's label will, at least initially, be for psorriasis. They may take some or much of Humiras market for that indication - but it will be some time before they take large market share overall. It would take ctix years to complete the multiple phase 3 studies required to grab the diverse market Humira does. As far as off-label use goes for non-psoriasis indications, few clinicians will travel off label with a new drug. Since standard of practice inhibits such risk - most will stay on label until enough evidence accumulates to support off label use. Prurisol may be an excellent drug - but it will be years before it  compares to Humira's profits.