Drug interactions
Levothyroxine + Sodium iodide i-131
Severity: Major
Levothyroxine and Sodium iodide i-131: major interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Exogenous thyroid hormone suppresses TSH and reduces thyroid tissue iodine uptake, so less radioiodine reaches the thyroid or thyroid cancer remnants. This can make diagnostic uptake studies unreliable and reduce the therapeutic effect of I-131.
What this interaction means in plain words
Levothyroxine and Sodium iodide i-131 can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Levothyroxine suppresses TSH-driven iodide uptake by thyroid tissue, lowering I-131 accumulation.
What to do
Withhold levothyroxine for the period specified in the radioiodine protocol (or use recombinant TSH stimulation) before I-131 dosing. Restart thyroid hormone after treatment as directed by the nuclear medicine or endocrine team.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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Other interactions of Levothyroxine
- Cholestyramine + Levothyroxine Major
- Levothyroxine + Tiratricol Major
- Adrenaline-articaine + Levothyroxine Moderate
- Alogliptin-metformin + Levothyroxine Moderate
- Amitriptyline + Levothyroxine Moderate
- Amobarbital + Levothyroxine Moderate
Frequently asked questions
Can I take Levothyroxine with Sodium iodide i-131?
MediHelp rates the interaction as major. Levothyroxine and Sodium iodide i-131 can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Exogenous thyroid hormone suppresses TSH and reduces thyroid tissue iodine uptake, so less radioiodine reaches the thyroid or thyroid cancer remnants. This can make diagnostic uptake studies unreliable and reduce the therapeutic effect of I-131.
How serious is the interaction between Levothyroxine and Sodium iodide i-131?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Withhold levothyroxine for the period specified in the radioiodine protocol (or use recombinant TSH stimulation) before I-131 dosing. Restart thyroid hormone after treatment as directed by the nuclear medicine or endocrine team.
What other medicines interact with Levothyroxine?
MediHelp also lists interactions of Levothyroxine with, for example, Cholestyramine, Tiratricol, Adrenaline-articaine. The full list is on the Levothyroxine page.
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