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Morphine toxicity in renal impairment — FRCA Final MCQ

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HardPain MedicineMorphine toxicity in renal impairmentFRCA Final

A 74-year-old woman with stage 4 chronic kidney disease has painful bone metastases. She becomes drowsy and myoclonic after escalating oral morphine. Respiratory rate is 12/min and pain remains poorly controlled. What is the most likely cause of the complication?

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Correct answer: B — Accumulation of renally cleared morphine metabolites

Morphine metabolites accumulate in renal impairment and can cause sedation, myoclonus and neurotoxicity. Allergy would present with urticaria, bronchospasm or hypotension rather than myoclonus after dose escalation. Serotonin syndrome is not typical of morphine. Opioid rotation to a renal-safer agent with specialist palliative care input is appropriate.

Reference: BNF opioid prescribing in renal impairment; NICE palliative care guidance