Drug interactions
Methimazole + Sodium iodide i-131
Severity: Major
Methimazole 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
Antithyroid drugs reduce thyroid uptake of radioiodine, so the therapeutic radiation dose delivered to the gland may be inadequate. Treatment failure or the need for repeat dosing may result.
What this interaction means in plain words
Methimazole 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
Methimazole inhibits thyroid peroxidase and hormone synthesis, which lowers thyroidal radioiodine uptake and retention.
What to do
Stop methimazole several days before I-131 administration, typically 3 to 4 days per labeling, and do not give them together. Restart afterward according to the treating specialist's plan and monitor thyroid function.
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 Methimazole
- Carbamazepine + Methimazole Major
- Clozapine + Methimazole Major
- Methimazole + Propylthiouracil Major
- Iodinated glycerol + Methimazole Moderate
- Iodine + Methimazole Moderate
- Lycopus + Methimazole Moderate
Frequently asked questions
Can I take Methimazole with Sodium iodide i-131?
MediHelp rates the interaction as major. Methimazole 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. Antithyroid drugs reduce thyroid uptake of radioiodine, so the therapeutic radiation dose delivered to the gland may be inadequate. Treatment failure or the need for repeat dosing may result.
How serious is the interaction between Methimazole 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: Stop methimazole several days before I-131 administration, typically 3 to 4 days per labeling, and do not give them together. Restart afterward according to the treating specialist's plan and monitor thyroid function.
What other medicines interact with Methimazole?
MediHelp also lists interactions of Methimazole with, for example, Carbamazepine, Clozapine, Propylthiouracil. The full list is on the Methimazole page.
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