Drug interactions
Methimazole + Theophylline
Severity: Moderate
Methimazole and Theophylline: moderate interaction.
Last updated Sources: US FDA label
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
Theophylline clearance is increased in hyperthyroidism and falls as thyroid function normalizes with methimazole. Theophylline levels can therefore rise over weeks, with a risk of toxicity.
What this interaction means in plain words
Methimazole and Theophylline can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Methimazole belongs to Endocrine; Theophylline belongs to Respiratory.
Why it happens
Correction of the hyperthyroid state reduces the hepatic metabolism of theophylline.
What to do
Monitor theophylline levels as the patient becomes euthyroid and reduce the dose as needed.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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References
- methimazole - FDA drug label (DailyMed) — openFDA / DailyMed
Other interactions of Theophylline
- Riociguat + Theophylline Contraindicated
- Adenosine + Theophylline Major
- Apalutamide + Theophylline Major
- Bupropion + Theophylline Major
- Carvedilol + Theophylline Major
- Cimetidine + Theophylline Major
Other interactions of Methimazole
- Carbamazepine + Methimazole Major
- Clozapine + Methimazole Major
- Methimazole + Propylthiouracil Major
- Methimazole + Sodium iodide i-131 Major
- Iodinated glycerol + Methimazole Moderate
- Iodine + Methimazole Moderate
Frequently asked questions
Can I take Methimazole with Theophylline?
MediHelp rates the interaction as moderate. Methimazole and Theophylline can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Theophylline clearance is increased in hyperthyroidism and falls as thyroid function normalizes with methimazole. Theophylline levels can therefore rise over weeks, with a risk of toxicity.
How serious is the interaction between Methimazole and Theophylline?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor theophylline levels as the patient becomes euthyroid and reduce the dose as needed.
What other medicines interact with Theophylline?
MediHelp also lists interactions of Theophylline with, for example, Riociguat, Adenosine, Apalutamide. The full list is on the Theophylline page.
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