Levothyroxine with iron calcium — GPhC CRA MCQ

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HardEndocrine TherapeuticsLevothyroxine with iron calciumGPhC CRA

A patient takes levothyroxine before breakfast but also takes ferrous sulfate and calcium carbonate at the same time. Thyroid control has become unstable. Which schedule is most appropriate?

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Correct answer: C — Separate levothyroxine from both iron and calcium by four hours

Separate levothyroxine from both iron and calcium by four hours: Both polyvalent-cation products can bind levothyroxine and reduce absorption; a consistent separated schedule supports interpretable thyroid monitoring. Take all three medicines together with the same breakfast each day: Consistent under-absorption is not therapeutically acceptable and may remain variable. Separate iron but continue calcium with the fasting levothyroxine dose: Calcium also reduces levothyroxine absorption. Increase levothyroxine on days when either mineral supplement is taken: Self-adjusted dose compensation is unreliable and can produce over-treatment when timing changes. Stop both mineral supplements and continue the current levothyroxine schedule: The interaction can usually be managed by timing rather than abandoning indicated therapy.

Reference: BNF: levothyroxine sodium: https://bnf.nice.org.uk/drugs/levothyroxine-sodium/; BNF: ferrous sulfate: https://bnf.nice.org.uk/drugs/ferrous-sulfate/; BNF: calcium carbonate: https://bnf.nice.org.uk/drugs/calcium-carbonate/; Levothyroxine tablets UK summary of product characteristics: https://www.medicines.org.uk/emc/product/5682/smpc