A 32-year-old man with a 3-year history of ulcerative colitis maintained on mesalamine presents with a 2-week history of low back pain and morning stiffness lasting about 60 minutes. He notes improvement with exercise and exacerbation at rest. He also reports a swollen, painful right knee. Physical examination reveals tenderness over both sacroiliac joints and an effusion of the right knee. Laboratory studies show elevated CRP and ESR. Pelvic X-ray demonstrates bilateral sacroiliitis. Which of the following is the most appropriate next step in management?