Drug interactions
Methimazole + Propylthiouracil
Severity: Major
Methimazole and Propylthiouracil: 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
Both are thionamide antithyroid drugs with the same therapeutic action, so combining them offers no benefit. Each carries a risk of agranulocytosis, hepatotoxicity and other adverse effects, and duplication may add to this risk.
What this interaction means in plain words
Methimazole and Propylthiouracil 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.
Methimazole belongs to Endocrine; Propylthiouracil belongs to Endocrine.
Why it happens
Therapeutic duplication with additive adverse effects, including myelosuppression, from two thionamides.
What to do
Avoid concurrent use; use a single thionamide and monitor blood counts and liver function, with prompt evaluation of fever or sore throat.
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 Propylthiouracil
Other interactions of Methimazole
- Carbamazepine + Methimazole Major
- Clozapine + Methimazole Major
- Methimazole + Sodium iodide i-131 Major
- Iodinated glycerol + Methimazole Moderate
- Iodine + Methimazole Moderate
- Lycopus + Methimazole Moderate
Frequently asked questions
Can I take Methimazole with Propylthiouracil?
MediHelp rates the interaction as major. Methimazole and Propylthiouracil 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. Both are thionamide antithyroid drugs with the same therapeutic action, so combining them offers no benefit. Each carries a risk of agranulocytosis, hepatotoxicity and other adverse effects, and duplication may add to this risk.
How serious is the interaction between Methimazole and Propylthiouracil?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid concurrent use; use a single thionamide and monitor blood counts and liver function, with prompt evaluation of fever or sore throat.
What other medicines interact with Propylthiouracil?
MediHelp also lists interactions of Propylthiouracil with, for example, Carbamazepine, Clozapine, Pexidartinib. The full list is on the Propylthiouracil page.
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