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Luminal Agent for Amoebiasis — SCE Infectious Diseases MCQ

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EasyTropical & Imported InfectionsLuminal Agent for AmoebiasisSCE Infectious Diseases

A 28-year-old man returns from a gap year in South America with a 2-month history of bloody diarrhoea and abdominal pain. Colonoscopy shows flask-shaped ulcers in the caecum and ascending colon. Biopsy shows trophozoites with ingested erythrocytes. Stool antigen test for Entamoeba histolytica is positive. He is treated with Metronidazole. Why must a luminal agent be added?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: A — Metronidazole kills tissue trophozoites but does not eliminate intraluminal cysts — without a luminal agent (Diloxanide Furoate or Paromomycin), cyst shedding continues with risk of relapse and transmission

Metronidazole is a tissue amoebicide — it effectively kills trophozoites in the intestinal wall, liver, and other tissues. However, it achieves insufficient luminal concentrations to eliminate intraluminal cyst forms. Without a follow-on luminal agent, up to 50% of patients relapse from residual cysts. Diloxanide Furoate 500 mg TDS for 10 days (or Paromomycin 500 mg TDS for 7 days) is given AFTER completing Metronidazole to eradicate luminal cysts. This two-step approach is mandatory for all invasive amoebiasis.

Reference: BNF 2024 – Amoebiasis; WHO 2023 – Amoebiasis