A 32-year-old man with a 5-year history of ulcerative colitis presents to the clinic with a 2-week history of painful swelling in his right knee and left ankle. He describes the arthritis as migratory and notes that joint pain flares coincide with his colitis exacerbations. He denies back pain, eye irritation, or skin rashes. His medications include mesalamine and as-needed prednisone during flares. On examination, the right knee and left ankle are warm, erythematous, and tender with effusion. Laboratory studies show ESR 45 mm/hr (elevated), CRP 3.2 mg/dL (elevated), negative rheumatoid factor, and HLA-B27 negative. Colonoscopy performed 3 months ago showed moderate activity. What is the most appropriate next step in management of his arthritis?