TNF and psoriatic arthritis: Etanercept: The TNF-α inhibitor etanercept is FDA-approved for the treatment of adults and children aged four years and older with chronic moderate-to-severe plaque psoriasis, as well as for the treatment of psoriatic arthritis. The starting dose for adults is a 50 mg subcutaneous injection twice per week for three consecutive months, followed by a 50 mg injection once per week as maintenance therapy.