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Lithium toxicity — RACP Adult Medicine MCQ

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HardClinical pharmacology and toxicologyLithium toxicityRACP Adult Medicine

A 70-year-old man taking lithium for bipolar disorder presents with tremor, ataxia and diarrhoea after starting ibuprofen for back pain. Creatinine has risen from 86 to 152 micromol/L and lithium concentration is elevated. What is the most likely cause?

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Correct answer: C — Reduced renal lithium clearance precipitated by NSAID use and dehydration

Lithium is renally cleared, and NSAIDs plus dehydration can reduce clearance and precipitate toxicity. Serotonin syndrome and anticholinergic poisoning have different autonomic and neuromuscular patterns. Lithium is not hepatically metabolised, and stroke would not explain the elevated concentration and systemic toxicity.

Reference: Australian Medicines Handbook; Poisons Information Centre guidance