A 22-year-old nonbinary patient with a 7-year history of Crohn's ileocolitis is admitted with worsening abdominal pain, diarrhea and fever. The patient has been taking 6-mercaptopurine and has never taken a biologic agent. WBC is elevated at 19. CT abdomen reveals an 8 cm abscess in the left abdomen adjacent to the sigmoid colon. In addition to starting antibiotics, which of the following is most appropriate at this time?