Lithium Toxicity — MRCPsych Paper B MCQ

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ModerateMood DisordersLithium ToxicityMRCPsych Paper B

A 40-year-old man taking lithium carbonate 800 mg daily for bipolar disorder develops vomiting and diarrhoea over 3 days. He now has a coarse tremor and confusion. A plasma lithium concentration is 2.1 mmol/L. What is the priority management?

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Correct answer: C — Stop lithium, admit urgently, give intravenous isotonic fluids and seek specialist toxicology or renal advice

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

The correct answer is B. This patient has symptomatic lithium toxicity, with gastrointestinal disturbance, coarse tremor and confusion, together with a markedly elevated lithium concentration. Lithium must be stopped immediately, and he requires urgent hospital management with assessment and correction of fluid and electrolyte depletion, serial lithium measurements, renal-function monitoring and specialist toxicology or renal advice. Haemodialysis is considered according to the severity of neurological toxicity, renal function, clinical course and serial concentrations rather than a single rigid concentration threshold. Dose reduction or observation alone (A and E) is unsafe in symptomatic toxicity. Propranolol (C) may treat a benign lithium-associated tremor but not toxic neurological features. Switching mood stabilisers (D) does not address the acute poisoning and should be considered only after medical stabilisation.

Reference: Electronic Medicines Compendium, Lithium Carbonate Essential Pharma 250 mg film-coated tablets, SmPC sections 4.4 and 4.9, updated 2025. https://www.medicines.org.uk/emc/product/10828/smpc