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Levothyroxine and iron — GPhC CRA MCQ

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ModerateEndocrine TherapeuticsLevothyroxine and ironGPhC CRA

A 66-year-old woman taking levothyroxine 100 micrograms each morning starts ferrous sulfate 200mg twice daily for iron deficiency anaemia. Her TSH has risen and she feels tired again. What is the most important interaction to flag?

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Correct answer: B — Iron can reduce levothyroxine absorption and doses should be separated

Iron salts can bind levothyroxine in the gastrointestinal tract and reduce absorption. Separating administration times helps minimise the interaction and thyroid function may need rechecking. The raised TSH and return of symptoms fit reduced thyroid hormone exposure. Tea can reduce iron absorption and is not a solution.

Reference: BNF