A 70-year-old patient with chronic renal failure (eGFR 15) requires opioid analgesia for cancer pain. Which opioid should be avoided due to accumulation of a neuroexcitatory metabolite?
- A Morphine ✓
- B Fentanyl
- C Methadone
- D Buprenorphine
Correct answer: A. Morphine
Explanation
Morphine is extensively metabolised to morphine-6-glucuronide (M6G, potent analgesic) and morphine-3-glucuronide (M3G), both renally excreted. In renal failure, M3G accumulates and is neuroexcitatory, causing allodynia, hyperalgesia, myoclonus and seizures. Fentanyl is metabolised to inactive norfentanyl and is safer in renal failure. Buprenorphine is also considered safe in CKD as its glucuronide metabolites are less pharmacologically active. Methadone is primarily hepatically metabolised.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.