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St John's wort and combined hormonal contraception — GPhC CRA MCQ

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ModerateDrug InteractionsSt John's wort and combined hormonal contraceptionGPhC CRA

A 73-year-old woman taking lithium carbonate modified-release tablets attends with tremor, diarrhoea and unsteadiness after a week of poor oral intake from gastroenteritis. Her daughter says she also started ibuprofen for back pain. The next lithium dose is due this evening. What monitoring is required?

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Correct answer: D — Urgent lithium concentration, renal function and electrolytes

Tremor, diarrhoea and ataxia are concerning for lithium toxicity, and dehydration plus NSAID use can raise lithium concentrations. Urgent lithium level, renal function and electrolytes are needed alongside clinical assessment. The pharmacist should advise urgent care and withholding lithium pending review.

Reference: BNF; FSRH guidance