How should an adult with newly diagnosed ulcerative colitis or Crohn disease be managed based on disease severity (mild‑moderate vs moderate‑severe) and anatomical location (rectum/left colon, ileum, colon, extensive or penetrating disease)?

Management of Inflammatory Bowel Disease in Adults

Ulcerative Colitis

Mild-to-Moderate Extensive or Left-Sided Disease

Start oral mesalamine 2–4 g daily (once-daily dosing preferred) as first-line therapy for all patients with mild-to-moderate ulcerative colitis extending beyond the rectum. 1, 2

• Mesalamine achieves endoscopic remission rates comparable to anti-TNF therapy and should be continued indefinitely for maintenance in all patients with left-sided or extensive disease 3, 4
• Balsalazide 6.75 g daily is an equivalent alternative 1
• Olsalazine 1.5–3 g daily has higher diarrhea rates in pancolitis and is best reserved for left-sided disease 1

If inadequate response after 2–4 weeks, add oral prednisolone 40 mg daily with gradual taper over 8 weeks. 1, 2

• More rapid tapering (< 8 weeks) is associated with early relapse 1, 2
• Consider adding topical mesalamine or corticosteroid suppositories/enemas for troublesome rectal symptoms, though they are unlikely to be effective as monotherapy 1

For patients requiring more than one course of corticosteroids per year, escalate to azathioprine 1.5–2.5 mg/kg/day or mercaptopurine 0.75–1.5 mg/kg/day as steroid-sparing agents. 1, 3, 4

• Check complete blood count within 4 weeks of starting thiopurines, then every 6–12 weeks to detect neutropenia 3, 4
• Never use corticosteroids (including budesonide) for long-term maintenance—they are ineffective and carry significant toxicity 4

Distal Disease (Proctitis and Proctosigmoiditis)

Initiate topical mesalamine suppositories (1 g daily for proctitis) or enemas (1–4 g daily for proctosigmoiditis) as first-line therapy. 1

• For patients who relapse more than once yearly despite topical therapy, add oral mesalamine 2–4 g daily 1, 4
• Maintenance therapy with aminosalicylates reduces relapse risk and may lower colorectal cancer risk 1, 4
• Discontinuation may be considered only for distal disease in remission ≥ 2 years in patients averse to medication 1, 4

Severe Ulcerative Colitis (Hospitalization Required)

Admit immediately and start intravenous hydrocortisone 400 mg/day or methylprednisolone 60 mg/day without waiting for stool culture results. 1, 2

• Obtain stool cultures for bacterial pathogens, C. difficile toxin, and parasites, but do not delay corticosteroids 2
• Provide IV fluids, electrolyte replacement, blood transfusion to maintain hemoglobin > 10 g/dL, and subcutaneous heparin for VTE prophylaxis 2
• Ensure joint management by gastroenterology and colorectal surgery from admission; counsel patients about 25–30% colectomy risk 1, 2

By day 3, assess response: > 8 stools/day or 3–8 stools/day with CRP > 45 mg/L predicts ≈ 85% colectomy rate and mandates rescue therapy. 2

• Rescue options: infliximab 5 mg/kg IV at weeks 0,2,6 or ciclosporin 2 mg/kg/day IV 1, 2
• Urgent surgery is indicated for toxic megacolon not improving after 24–48 hours, colonic perforation, massive hemorrhage with hemodynamic instability, or failure of rescue therapy after 4–7 days 2

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Crohn's Disease

Mild Ileocolonic or Colonic Disease

Start high-dose mesalamine 4 g daily as initial therapy for mild ileocolonic Crohn's disease. 1, 2, 3

• Sulfasalazine 4 g daily is effective for active colonic disease but has higher side effect rates; reserve for selected patients with reactive arthropathy 1
• Topical mesalamine may be effective in left-sided colonic Crohn's disease of mild-to-moderate activity 1

Moderate-to-Severe Ileocolonic or Colonic Disease

Prescribe oral prednisolone 40 mg daily with an 8-week taper for patients with moderate-to-severe disease or those who failed mesalamine. 1, 2, 3

• For isolated ileocecal moderate disease, budesonide 9 mg daily is an alternative, though marginally less effective than prednisolone 1, 2, 3
• Rapid taper (< 8 weeks) is linked to early relapse 1, 2

For steroid-dependent disease (requiring > 1 course/year), initiate azathioprine 1.5–2.5 mg/kg/day or mercaptopurine 0.75–1.5 mg/kg/day as steroid-sparing agents. 1, 3, 4

• These agents have slow onset of action (8–12 weeks) and should be used adjunctively, not as sole therapy for active disease 1
• Monitor CBC within 4 weeks, then every 6–12 weeks 3
• Methotrexate IM 25 mg weekly for 16 weeks, then 15 mg weekly, is an alternative for chronic active disease 3

Severe Crohn's Disease (Hospitalization Required)

Administer intravenous hydrocortisone 400 mg/day or methylprednisolone 60 mg/day plus intravenous metronidazole because active disease is difficult to distinguish from septic complications. 1, 2

• Elemental or polymeric diets are less effective than corticosteroids but may be used in selected patients with contraindications to steroids or as adjunctive therapy 1
• Total parenteral nutrition is appropriate adjunctive therapy in complex fistulating disease 1

Infliximab 5 mg/kg is effective for severe disease but must be avoided in patients with obstructive symptoms. 1, 2, 3

• Active sepsis (e.g., abscess) is an absolute contraindication due to risk of overwhelming septicemia 1
• Screen for tuberculosis before initiating anti-TNF therapy 1

Penetrating or Fistulating Disease

Consider surgery for patients who have failed medical therapy; surgery may be appropriate as primary therapy in selected cases. 1, 3

• Resections must be limited to macroscopic disease only 3
• Never perform primary anastomosis in the presence of sepsis and malnutrition 3

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Critical Decision Points by Anatomical Location

Rectum Only (Proctitis)

• UC: Topical mesalamine suppositories 1 g daily 1
• CD: Topical mesalamine may be effective 1

Left Colon (Up to Splenic Flexure)

• UC: Oral mesalamine 2–4 g daily ± topical therapy 1
• CD: Topical mesalamine for mild-moderate; oral prednisolone for moderate-severe 1

Extensive Disease (Beyond Splenic Flexure)

• UC: Oral mesalamine 2–4 g daily; escalate to prednisolone if inadequate response 1
• CD (ileocolonic): Mesalamine 4 g daily for mild; prednisolone or budesonide for moderate-severe 1, 2, 3

Isolated Ileal Disease

• CD: Budesonide 9 mg daily for moderate disease; prednisolone 40 mg for severe 1, 2, 3

Penetrating/Fistulating Disease

• CD: IV steroids + metronidazole; consider infliximab or surgery 1, 2

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Maintenance Therapy After Remission

Continue aminosalicylates indefinitely for all UC patients with left-sided or extensive disease, and for those with distal disease who relapse > 1×/year. 1, 4

• Maintenance therapy reduces relapse risk and may provide protection against colorectal cancer 1, 4
• For Crohn's disease, azathioprine or mercaptopurine are first-line maintenance agents, particularly for steroid-dependent patients 3, 4
• Smoking cessation is the single most important intervention for Crohn's disease and should be strongly emphasized with active support 4

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Monitoring and Treatment Targets

Never rely on symptoms alone; always use objective inflammatory markers (fecal calprotectin, CRP, endoscopy) to guide treatment decisions. 3

• Perform colonoscopy at 8 years from diagnosis for surveillance of dysplasia, with subsequent intervals individualized based on risk factors 4, 5
• Monitor vital signs four times daily, stool frequency, and abdominal examination in hospitalized patients 2
• Repeat laboratory panel (CBC, ESR/CRP, electrolytes, albumin) every 24–48 hours in severe disease 2

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Common Pitfalls to Avoid

• Do not delay corticosteroids while awaiting stool microbiology in suspected severe colitis 2
• Avoid rapid prednisolone tapering (< 8 weeks)—it causes early relapse 1, 2
• Do not use infliximab in Crohn's patients with obstructive symptoms 1, 2
• Before escalating therapy in Crohn's disease, consider alternative causes: bacterial overgrowth, bile salt malabsorption, fibrotic strictures 1, 2
• Never use corticosteroids for maintenance therapy in either UC or Crohn's disease 4