PAMORA for OIC — RACP Adult Medicine MCQ

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ModerateClinical PharmacologyPAMORA for OICRACP Adult Medicine

A 70-year-old man with chronic pain on long-term codeine develops constipation refractory to standard laxatives (senna, docusate, macrogol). He is unable to change his opioid. What peripherally-acting opioid antagonist may help?

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Correct answer: A — Loperamide

Opioid-induced constipation (OIC) refractory to standard laxatives may respond to peripherally-acting mu-opioid receptor antagonists (PAMORAs) – naloxegol (oral) or methylnaltrexone (SC). These drugs block mu-opioid receptors in the GI tract without crossing the BBB, thus not reversing central analgesia. Naloxegol (25 mg oral daily) is PBS-listed in Australia for OIC refractory to ≥2 laxatives. It should not be used with strong CYP3A4 inhibitors. Oral naloxone (available as oxycodone/naloxone combination – Targin) provides local GI opioid antagonism with systemic opioid analgesia (naloxone is extensively first-pass metabolised so systemic levels remain negligible).

Reference: AMH – 2025 – Opioid Adverse Effect Management; PBS – 2025 – Naloxegol Listing