Lithium and Dehydration — MRCPsych Paper B MCQ
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Correct answer: A — Withhold lithium, seek urgent clinical assessment and blood tests, and restart only on clinical advice
The correct answer is A. Profuse vomiting and diarrhoea with inability to maintain fluid intake creates substantial fluid and sodium depletion, reducing renal lithium clearance and increasing the risk of accumulation and toxicity. Lithium should therefore be withheld while urgent medical assessment is arranged, including a serum lithium concentration, urea and electrolytes, and renal function. Restarting should follow clinical or specialist advice rather than occur automatically when symptoms improve. Continuing the usual dose, even with anti-diarrhoeal treatment or additional dietary salt, does not safely address possible toxicity. Empirical dose reduction is also inadequate because lithium has a narrow therapeutic index and management should be guided by clinical assessment and urgent investigations.
Reference: NHS Specialist Pharmacy Service. Lithium monitoring—Risk of toxicity: action required. Fully reviewed and republished 6 December 2024. https://sps.nhs.uk/monitorings/lithium-monitoring/