Selpercatinib and Famotidine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Selpercatinib
Famotidine
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
Reduced selpercatinib exposure, reduced anti-tumor activity and an increased risk of QT interval prolongation
Interaction Deep Dive
Selpercatinib is associated with QT-interval prolongation that may necessitate dosage reduction and famotidine is an H2-antagonist known to prolong the QT interval. Avoid coadministration of selpercatinib with an H2-antagonists (eg, famotidine) may reduce selpercatinib exposure and result in diminished anti-tumor activity. In a pharmacokinetic study, raNITIdine (an H2-antagonist) taken 10 hours prior and 2 hours after selpercatinib on an empty stomach did not significantly effect exposure. If coadministration is necessary, take each selpercatinib dose fasting and famotidine 10 hours prior to or 2 hours after selpercatinib to maintain desired selpercatinib exposure. Assess QT interval, electrolytes and TSH at baseline and periodically during treatment, adjusting frequency based upon risk factors including diarrhea. Correct hypokalemia, hypomagnesemia, and hypocalcemia prior to initiating selpercatinib and during treatment. Withhold and reduce the dose or permanently discontinue selpercatinib based on severity1.
Why it happens (mechanism)
Changes in gastric pH; additive QT interval prolongation
Literature reports
1 report — tap to read
a) In a pharmacokinetic study, multiple daily doses of raNITIdine (an H2-antagonist) taken 10 hours prior and 2 hours after selpercatinib on an empty stomach did not significantly effect selpercatinib exposure 1.
Common questions
Can I take Selpercatinib and Famotidine together?
Reduced selpercatinib exposure, reduced anti-tumor activity and an increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.
How serious is the Selpercatinib and Famotidine 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Selpercatinib or Famotidine 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: RETEVMO(R) oral capsules, tablets, selpercatinib oral capsules, tablets. Lilly USA LLC (per FDA), Indianapolis, IN, 2024. DailyMed
Keep reading about Selpercatinib
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