Theophylline and Azithromycin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Theophylline
Azithromycin
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increase serum theophylline concentrations
Interaction Deep Dive
Azithromycin administered as 500 mg on day 1 and 250 mg daily on days 2 through 5 did not affect the pharmacokinetics or plasma levels of a single intravenous dose of theophylline. The effect of azithromycin coadministration on steady-state theophylline levels is unknown. However, the combined use of macrolide antibiotics and theophylline has been associated with increases in serum concentrations of theophylline. Therefore, concurrent use of theophylline and azithromycin should be done with close monitoring of plasma theophylline levels1.
Why it happens (mechanism)
Unknown
Common questions
Can I take Theophylline and Azithromycin together?
Increase serum theophylline concentrations Always confirm with your pharmacist or prescriber before making any change.
How serious is the Theophylline and Azithromycin interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Theophylline or Azithromycin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (1)
- Product Information: Zithromax(R), azithromycin. Pfizer Labs, New York, NY, 2001. DailyMed
Keep reading about Theophylline
Keep reading about Azithromycin
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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