What is the recommended management for a patient undergoing pelvic or abdominal radiotherapy who develops diarrhoea?

Management of Radiotherapy-Induced Diarrhoea

Start loperamide immediately at the first sign of diarrhoea during pelvic or abdominal radiotherapy, continue it throughout the entire radiation treatment course, and add probiotics from day one of radiation to reduce both acute and severe diarrhoea. 1, 2

Acute Radiation-Induced Diarrhoea (During RT or Within 3 Months)

First-Line Pharmacologic Management

Loperamide is the primary antidiarrhoeal agent and should be continued for the duration of radiotherapy due to repeated intestinal mucosal injury from ongoing radiation exposure. 1 This approach differs from chemotherapy-induced diarrhoea where loperamide may be stopped after symptom resolution.

• Loperamide dosing must not exceed recommended doses due to cardiac risks including QT prolongation, Torsades de Pointes, and sudden death. 3
• Avoid loperamide in combination with QT-prolonging drugs (Class 1A or III antiarrhythmics, certain antipsychotics, moxifloxacin, methadone). 3
• Discontinue loperamide immediately if constipation, abdominal distention, or ileus develops, as prolonged use increases risk of toxic megacolon. 3

Probiotics for Prevention and Treatment

Add probiotics starting on the first day of radiotherapy to significantly reduce moderate-to-severe diarrhoea. 4, 5, 6

• Standard-dose probiotics (Lactobacillus acidophilus and Bifidobacterium longum at 1.3 billion CFU twice daily) reduce grade 2-4 diarrhoea, with 35% of patients remaining diarrhoea-free at 60 days versus only 17% with placebo (hazard ratio 0.69, p=0.04). 6
• In patients with prior pelvic surgery, standard-dose probiotics reduce severe grade 4 diarrhoea from 26% to 3% (p=0.03). 6
• VSL#3 (one bag three times daily) reduces overall toxicity from 50.6% to 30.5% and severe grade 3-4 toxicity from 28 to 7 patients in radiation cohorts. 5
• The evidence for probiotics is strongest among nutritional interventions, with multiple high-quality studies demonstrating benefit. 7

Dietary Modifications

Eliminate lactose-containing products immediately, as lactose malabsorption develops as a direct side effect of pelvic radiation and correlates with the volume of small bowel exposed. 8

• Recommend 8-10 large glasses of clear liquids daily to prevent dehydration. 9
• Advise small, frequent meals consisting of bananas, rice, applesauce, toast, and plain pasta (BRAT diet). 9
• Avoid alcohol and high-osmolar dietary supplements. 9

Fluid and Electrolyte Management

Aggressive IV fluid resuscitation is mandatory for any patient with signs of dehydration, weakness, or hemodynamic compromise. 9, 3

• Dehydration is common and potentially life-threatening, particularly in patients under 6 years of age who show greater variability in response. 3
• Monitor daily stool frequency, consistency, volume, and reassess renal function and electrolytes daily until normalized. 9

Classification and Escalation Criteria

Complicated Diarrhoea Requiring Hospitalization

Classify as "complicated" and hospitalize if any of the following are present: 9

• Moderate to severe cramping
• Grade 2 nausea/vomiting
• Decreased performance status or weakness
• Fever, sepsis, or neutropenia
• Frank bleeding
• Dehydration
• Any grade 3-4 diarrhoea

Workup for Complicated Cases

Obtain immediately: 9

• Complete blood count (assess neutropenia/myelosuppression)
• Comprehensive metabolic panel (electrolytes, renal function)
• Stool studies for blood, fecal leukocytes, C. difficile, Salmonella, E. coli, Campylobacter

Advanced Management for Complicated Cases

Start octreotide 100-150 μg subcutaneously three times daily for complicated radiation-induced diarrhoea that fails loperamide. 9, 2

Initiate empiric fluoroquinolone therapy for 7 days in complicated cases due to increased risk of infectious complications. 9

Chronic Radiation-Induced Diarrhoea (Beyond 3 Months)

Recognition and Pathophysiology

Chronic diarrhoea after pelvic radiation represents "pelvic radiation disease"—progressive ischemia and fibrosis rather than simple diarrhoea—and requires different management than acute toxicity. 1

• Approximately 90% of patients develop permanent bowel habit changes after pelvic radiation, with 50% experiencing quality-of-life impact from gastrointestinal symptoms. 1, 4
• Symptoms may not manifest for 20-30 years after radiation in some patients. 1
• Chronic symptoms result from arteriole endarteritis, submucosal fibrosis, and telangiectasias. 4

Evaluation for Alternative Causes

Do not assume all post-radiation diarrhoea is purely radiation-induced. Evaluate systematically for: 1, 4

• C. difficile infection
• Bile salt malabsorption (from ileal dysfunction)
• Pancreatic insufficiency
• Lactose intolerance (persistent in 5% of patients)
• Small bowel bacterial overgrowth
• Strictures

Treatment Approach for Chronic Radiation Proctitis

First-line: Optimize bowel function and stop anticoagulants/antiplatelet agents if medically safe. 4

Second-line: Sucralfate enemas administered via soft Foley catheter inserted rectally, with patient rolling through 360 degrees to coat entire rectal surface. 4

• Do not use oral sucralfate—it does not prevent acute diarrhoea and causes more gastrointestinal side effects including rectal bleeding compared to placebo. 4

Third-line: Topical anti-inflammatory therapy with sulfasalazine or mesalamine alone or combined with steroids for Grade 1/2 proctitis. 4

Fourth-line: Hyperbaric oxygen therapy if initial treatments fail, as it induces neovascularization and tissue reoxygenation with response in the majority of chronic proctitis patients. 4

Fifth-line: Argon plasma coagulation resolves bleeding in 80-90% of chronic proctitis cases with repeated applications. 4

Endoscopic Evaluation

Perform flexible sigmoidoscopy or colonoscopy to confirm radiation-induced telangiectasia and exclude alternative pathology. 4

• Avoid biopsy unless neoplastic process is strongly suspected, as radiation-damaged tissue has significantly increased complication risk. 4

Critical Pitfalls to Avoid

• Never continue loperamide beyond recommended doses due to cardiac toxicity risks including sudden death. 3
• Never use oral sucralfate for prevention—it is ineffective and harmful. 4
• Never assume severe acute toxicity has resolved—it can lead to "consequential late effects" (delayed radiation injury developing after severe acute injury). 1
• Never delay evaluation for infection—radiation patients have increased susceptibility to C. difficile and bacterial enterocolitis. 1, 9
• Never ignore weakness—it indicates dehydration and electrolyte derangement requiring aggressive IV management. 9