A 21-year-old man with a diagnosis of ulcerative colitis 1 year ago presents to the emergency department with abdominal pain, profuse diarrhea, and bloating. Flexible sigmoidoscopy 3 weeks ago demonstrated Mayo score of 3 for proctocolitis, after which he was started on oral prednisone 40 mg daily. Clostridium difficile testing was negative. He has made no improvement. He has lost 10 lbs in the past 2 weeks. His vital signs on presentation are: temperature 38.7 °C, heart rate 140 beats per minute, blood pressure 80/50 mmHg, and spO2 of 94% on room air. He is uncomfortable and pale with a mildly distended abdomen. His abdominal X-ray is shown below. His laboratory work demonstrates: normal range electrolytes, blood urea nitrogen (BUN) of 25 mg/dL, creatinine 1.1 mg/dL, white blood cell count of 25,000, hemoglobin (Hgb) 8.0 g/dL, hematocrit 24%, and platelet count of 370,000. What is the best next step in his care?