Levothyroxine under-replacement — GPhC CRA MCQ
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Correct answer: A — Check thyroid function and review levothyroxine after carbamazepine induction
Check thyroid function and review levothyroxine after carbamazepine induction: Enzyme induction can reduce levothyroxine exposure and increase replacement requirements; objective monitoring should guide any dose change. Stop levothyroxine because raised TSH indicates excessive thyroid-hormone replacement: A raised TSH generally indicates insufficient thyroid-hormone effect, not excess. Take levothyroxine and carbamazepine together to saturate the metabolic interaction: Co-administration timing does not overcome enzyme induction. Increase levothyroxine immediately before obtaining repeat thyroid-function results: The change must be individualised using results and clinical assessment. Stop carbamazepine abruptly and continue the existing levothyroxine dose: Abrupt withdrawal can precipitate seizures; the interaction is managed through monitoring and authorised adjustment.
Reference: BNF: levothyroxine sodium: https://bnf.nice.org.uk/drugs/levothyroxine-sodium/; BNF: carbamazepine: https://bnf.nice.org.uk/drugs/carbamazepine/