skip to main content

Lithium Toxicity from NSAID — MRCPsych Paper B MCQ

Instant feedback + full explanation. One question, done properly.

ModerateMood DisordersLithium Toxicity from NSAIDMRCPsych Paper B

A 30-year-old man with bipolar I disorder has been stable on lithium, with a usual 12-hour serum lithium concentration of 0.7 mmol/L. Five days after starting an NSAID for knee pain, he develops diarrhoea and a new hand tremor. His 12-hour serum lithium concentration is now 1.8 mmol/L. What is the priority action?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Withhold lithium and the NSAID and arrange immediate medical assessment

The correct answer is E. This is symptomatic lithium toxicity: the 12-hour lithium concentration is 1.8 mmol/L, with new diarrhoea and tremor and a marked rise from 0.7 mmol/L after starting an NSAID. NSAIDs can increase serum lithium concentrations by impairing its renal elimination. Lithium and the precipitating NSAID should be withheld, and immediate medical assessment arranged for U&Es and renal function, serial lithium concentrations, ECG monitoring where indicated, and fluid and electrolyte management. Dose reduction or delayed rechecking is unsafe because toxicity may progress. Propranolol may be considered for a benign lithium-associated tremor only after toxicity has been excluded. Loperamide treats neither the raised lithium concentration nor its cause. Stopping only the NSAID while continuing lithium is also inappropriate in a symptomatic patient with a concentration of 1.8 mmol/L.

Reference: Electronic Medicines Compendium, Lithium Carbonate Essential Pharma 250 mg film-coated tablets, SmPC sections 4.2, 4.5 and 4.9, updated 2025. https://www.medicines.org.uk/emc/product/10828/smpc