M3G Neuroexcitatory Seizures in Renal Failure — SCE Palliative Medicine MCQ

Correct answer: C — Morphine-3-glucuronide accumulation in renal failure

Explanation lettering: D = shown as A · C = shown as B · B = shown as C · A = shown as D

Correct answer: B. In severe renal impairment (eGFR 15 mL/min), morphine’s glucuronide metabolites accumulate. M3G is neuroexcitatory (causing seizures, myoclonus, hyperalgesia), whereas M6G is analgesic and sedative. The marked prolongation of M3G elimination and its known neurotoxicity make it the most likely cause. The scenario is characteristic of opioid‑related neuroexcitation rather than idiopathic epilepsy (A), benzodiazepine withdrawal (C), hypoglycaemia (D; not supported by liver failure and seizure pattern), or M6G accumulation (E; would cause sedation, not seizures). Apply this conclusion only to the clinical circumstances stated, with appropriate specialist review, contraindication checks, shared decision-making and follow-up. Reassess if the physiology, treatment response or competing risk changes. The competing options would require a different haemodynamic profile, diagnosis, procedural indication or risk balance from the one described here.

Reference: Morphine metabolism--pharmacokinetics and pharmacodynamics (PubMed 1997) and Kinetics of morphine in patients with renal failure (PubMed 1987). NHS England palliative care guidance on renal impairment monitoring (2020).: https://www.nice.org.uk/guidance/ng217/chapter/recommendations