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Lithium Monitoring — RACP Adult Medicine MCQ

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ModerateNeurologyLithium MonitoringRACP Adult Medicine

A 55-year-old man on lithium for bipolar disorder presents with fine tremor, polyuria, and polydipsia. Lithium trough level is 1.3 mmol/L (therapeutic range 0.6-1.0 mmol/L). eGFR is 55 mL/min/1.73m² (declining). TSH is 8.5 mU/L. What is the most appropriate management?

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Correct answer: D — Reduce lithium dose and recheck level in 5-7 days

Supratherapeutic lithium (>1.0 mmol/L) with toxicity symptoms (tremor) and declining renal function requires dose reduction with repeat level in 5-7 days (lithium has a long half-life ~18-36 hours). The hypothyroidism (TSH 8.5) and nephrogenic DI (polyuria, polydipsia) are chronic lithium effects requiring monitoring. Levothyroxine should be started for the hypothyroidism. Regular monitoring: lithium levels, renal function, TFTs, and calcium every 3-6 months.

Reference: AMH – 2025 – Lithium Monitoring; RANZCP 2024; eTG Psychotropic 2024