For subjects receiving methotrexate (MTX) treatment: MTX may be administered either orally or parenterally at doses not to exceed 25 mg/wk or 20 mg/m2/week (whichever is lower); participants must have taken MTX for 3 months and be at a stable dose for at least 6 weeks before baseline. Subjects taking MTX must be taking folic acid or folinic acid in accordance with local standards.