Opioid accumulation in renal failure — FFICM MCQ

Correct answer: C — Switch away from morphine and consider cautious naloxone if clinically needed

The correct answer is C, switch away from morphine and consider cautious naloxone if clinically needed. In AKI, morphine's active metabolite morphine-6-glucuronide is renally excreted and accumulates, causing delayed awakening, pinpoint pupils, bradypnoea and myoclonus, a classic opioid toxicity picture rather than primary neurological injury (consistent with the unchanged CT). Management is to stop the accumulating agent, switch to an opioid with less dependence on renal clearance (such as fentanyl or alfentanil) for ongoing analgesia, and use naloxone cautiously and titrated only if respiratory depression is significant, since abrupt full reversal can precipitate severe pain, hypertension, arrhythmia and withdrawal in a patient who has received a prolonged high-dose infusion. This approach directly treats the identified cause while avoiding further renal-dependent opioid accumulation. Why the other options are wrong: E. Restart morphine at a higher dose: this would worsen accumulation of morphine-6-glucuronide in the context of ongoing AKI, deepening toxicity rather than resolving it. D. Give flumazenil as definitive reversal: flumazenil antagonises benzodiazepines, not opioids, and would not address the pinpoint pupils, bradypnoea or myoclonus caused by morphine metabolite accumulation. B. Diagnose brainstem death immediately: brainstem death testing is invalid while a reversible drug effect (opioid accumulation) confounds the neurological examination; this must be excluded or cleared first. A. Start phenytoin as first-line treatment: the myoclonus here is opioid-induced and reversible with removal of the causative drug, not a primary seizure disorder requiring an anticonvulsant. Key point: In renal impairment, morphine's active metabolite accumulates causing pinpoint pupils, bradypnoea and myoclonus, so the priority is stopping the opioid (switching to a renally safer agent) with cautious titrated naloxone if needed, not reversing benzodiazepines or diagnosing brain death.

Reference: British National Formulary (BNF), Morphine: Renal impairment, prescribing cautions and dose adjustment; NICE BNF online (medicines complete), accessed via https://bnf.nice.org.uk/drugs/morphine/