Drug interactions
Cimetidine + Theophylline
Severity: Major
Cimetidine and Theophylline: major 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
Cimetidine reduces theophylline clearance and can substantially raise serum levels, risking nausea, tachycardia, arrhythmia and seizures. Theophylline has a narrow therapeutic index so this is clinically important.
What this interaction means in plain words
Cimetidine and Theophylline 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.
Cimetidine belongs to Gastrointestinal Tract; Theophylline belongs to Respiratory.
Why it happens
Cimetidine inhibits CYP1A2 (and CYP3A4), decreasing theophylline metabolism.
What to do
Prefer an alternative acid suppressant such as famotidine or a proton pump inhibitor. If combined, reduce the theophylline dose and monitor serum concentrations.
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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References
- Theophylline (Anhydrous) - 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
- Ciprofloxacin + Theophylline Major
Other interactions of Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Frequently asked questions
Can I take Cimetidine with Theophylline?
MediHelp rates the interaction as major. Cimetidine and Theophylline 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. Cimetidine reduces theophylline clearance and can substantially raise serum levels, risking nausea, tachycardia, arrhythmia and seizures. Theophylline has a narrow therapeutic index so this is clinically important.
How serious is the interaction between Cimetidine and Theophylline?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Prefer an alternative acid suppressant such as famotidine or a proton pump inhibitor. If combined, reduce the theophylline dose and monitor serum concentrations.
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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