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Lithium-thiazide interaction — GPhC CRA MCQ

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ModerateDrug InteractionsLithium-thiazide interactionGPhC CRA

A 48-year-old man presents to the pharmacy with a prescription for bendroflumethiazide 2.5 mg once daily for newly diagnosed hypertension. He also takes lithium 400 mg twice daily for bipolar disorder. What is the most appropriate action?

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Correct answer: D — Contact the prescriber as thiazide diuretics can increase lithium levels to toxic concentrations

Thiazide diuretics reduce renal clearance of lithium and can lead to lithium toxicity, which is potentially life-threatening. The BNF lists this as a significant interaction. The prescriber should be contacted to discuss an alternative antihypertensive that does not affect lithium levels, such as amlodipine. Patients should not adjust lithium doses independently.

Reference: BNF Drug Interactions