Irinotecan Toxicity — SCE Medical Oncology MCQ

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ModerateGI CancersIrinotecan ToxicitySCE Medical Oncology

A 65-year-old man with metastatic CRC is started on irinotecan-based chemotherapy. He develops severe prolonged diarrhoea. Early-onset diarrhoea (during infusion) differs from late-onset diarrhoea in mechanism. What causes early-onset irinotecan diarrhoea?

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Correct answer: D — Acute cholinergic syndrome — treat with atropine

Irinotecan causes two distinct types of diarrhoea: (1) early-onset (within 24 hours, often during infusion) — caused by cholinergic stimulation (mediated by acetylcholinesterase inhibition), presenting with diarrhoea, diaphoresis, abdominal cramping, rhinitis and lacrimation; treated with subcutaneous atropine 0.25-1 mg. (2) Late-onset (>24 hours) — caused by direct mucosal damage by SN-38 (active metabolite); treated with high-dose loperamide (4 mg then 2 mg every 2 hours for up to 48 hours).

Reference: BNF Irinotecan monograph; ESMO 2024 Supportive Care Guidelines