Erlotinib and Idelalisib: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Idelalisib
Erlotinib
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
Increased erlotinib exposure and risk of toxicity
Interaction Deep Dive
Concomitant use of erlotinib (a CYP3A4 substrate) with a strong CYP3A4 inhibitor may result in increased exposure of erlotinib increasing the risk for toxicity1. During in-vitro drug-interaction studies, coadministration of erlotinib and strong CYP3A4 inhibitors resulted in a 2.1- to 4.2-fold increase in erlotinib AUC and prolonged the erlotinib half-life up to 16-fold 3. Avoid concurrent use, however if use is required, reduce the dose of erlotinib. If severe reactions occur with concomitant use, reduce the erlotinib dose in 50 mg decrements 1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated erlotinib metabolism
Literature reports
2 reports — tap to read
a) During drug interaction studies, coadministration of erlotinib and ketoconazole (a strong CYP3A4 inhibitor) resulted in a 67% increase in erlotinib AUC 2.
b) During in-vitro drug interaction studies, coadministration of erlotinib and ketoconazole (a strong CYP3A4 inhibitor) resulted in a 2.1-fold increase in erlotinib AUC and a moderate 1.9-fold increase in the half-life of erlotinib. Coadministration of erlotinib and ritonavir (a strong CYP3A4 inhibitor) resulted in a 4.2-fold increase in erlotinib AUC and a 16-fold increase in the half-life of erlotinib 3.
Common questions
Can I take Erlotinib and Idelalisib together?
Increased erlotinib exposure and risk of toxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Erlotinib and Idelalisib 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 Erlotinib or Idelalisib 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 (3)
- Product Information: TARCEVA(R) oral tablets, erlotinib oral tablets. Genentech USA Inc (per FDA), South San Francisco, CA, 2016. DailyMed
- Product Information: TARCEVA(R) oral tablets, erlotinib oral tablets. OSI Pharmaceuticals, LLC (per FDA), Northbrook, IL, 2014. DailyMed
- Pillai VC, Venkataramanan R, Parise RA, et al: Ritonavir and efavirenz significantly alter the metabolism of erlotinib--an observation in primary cultures of human hepatocytes that is relevant to HIV patients with cancer. Drug Metab Dispos 2013; 41(10):1843-1851. PubMed
Keep reading about Idelalisib
Keep reading about Erlotinib
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.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist