Rifampin and Gefitinib: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Rifampin
Gefitinib
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
Decreased exposure of gefitinib
Interaction Deep Dive
Concomitant use of gefitinib, a CYP3A4 substrate, with a strong CYP3A4 inducer decreases the exposure of gefitinib. The dosage of gefitinib should be increased to 500 mg daily with coadministration. Once 7 days have passed since the discontinuation of the strong CYP3A4 inducer, the gefitinib dose should be reduced back to the recommended daily dose of 250 mg1.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of gefitinib
Common questions
Can I take Rifampin and Gefitinib together?
Decreased exposure of gefitinib Always confirm with your pharmacist or prescriber before making any change.
How serious is the Rifampin and Gefitinib interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Rifampin or Gefitinib 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 a safer alternative to one of these medications for me?
References (1)
- Product Information: IRESSA(R) oral tablets, gefitinib oral tablets. AstraZeneca Pharmaceuticals (per FDA), Wilmington, DE, 2015. DailyMed
Keep reading about Rifampin
Keep reading about Gefitinib
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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