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Opioid-induced Constipation — SCE Medical Oncology MCQ

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EasySupportive & Palliative OncologyOpioid-induced ConstipationSCE Medical Oncology

A 60-year-old man with advanced lung cancer and bone metastases has been on oral morphine for 3 months. He reports good pain control but severe constipation despite regular senna and docusate. He has not opened his bowels for 5 days. What additional laxative agent specifically targets opioid-induced constipation?

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Correct answer: A — Methylnaltrexone (subcutaneous)

Methylnaltrexone is a peripherally-acting µ-opioid receptor antagonist (PAMORA) that blocks opioid receptors in the gut without crossing the blood-brain barrier (preserving analgesia). It is specifically licensed for opioid-induced constipation refractory to conventional laxatives. Naloxegol (oral PAMORA) is an alternative. These agents should be used after adequate trial of conventional laxatives (stimulant + softener) has failed.

Reference: BNF Methylnaltrexone monograph; NICE CG140 Opioids in palliative care; ESMO 2024 Supportive Care Guidelines