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Levothyroxine-calcium interaction — GPhC CRA MCQ

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ModerateDrug InteractionsLevothyroxine-calcium interactionGPhC CRA

A 48-year-old woman with hypothyroidism takes levothyroxine 100 micrograms once daily. She has recently started taking calcium and vitamin D supplements for osteoporosis prevention. She mentions her fatigue has returned. What is the most likely explanation?

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Correct answer: A — Calcium supplements reduce the absorption of levothyroxine if taken at the same time

Calcium salts can reduce the absorption of levothyroxine from the gastrointestinal tract through chelation. The BNF advises separating administration of calcium supplements from levothyroxine by at least four hours. This patient's returning hypothyroid symptoms are likely due to reduced levothyroxine absorption caused by taking both supplements together. Advising separation of doses should resolve the issue.

Reference: BNF Drug Interactions