Drug Interaction Report

Flecainide and Vandetanib: Interaction Details

A pharmacist-reviewed analysis of the Flecainide and Vandetanib interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Flecainide

Tambocor®
+

Vandetanib

Caprelsa Caprelsa®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
LinkedIn
Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
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.

Of 300 documented Flecainide interactions, 270 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

An increased risk of QT interval prolongation and Torsades de pointes

Interaction Deep Dive

Vandetanib can prolong the QT interval in a concentration-dependent manner. Torsades de pointes, ventricular tachycardia, and sudden death have been reported in patients taking vandetanib. The concomitant administration of vandetanib and other drugs that prolong the QT interval, such as flecainide1, should be avoided. If these drugs must be coadministered, monitor ECG more frequently. If the corrected QT interval (Fridericia; QTcF) is greater than 500 milliseconds, discontinue therapy until QTcF returns to less than 450 milliseconds. Dosing can then be resumed at a reduced dose 2.

Why it happens (mechanism)

Additive effects on the QT interval prolongation

Common questions

Can I take Flecainide and Vandetanib together?

An increased risk of QT interval prolongation and Torsades de pointes Always confirm with your pharmacist or prescriber before making any change.

How serious is the Flecainide and Vandetanib 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 Flecainide or Vandetanib 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 (2)

  1. Product Information: flecainide acetate oral tablets, flecainide acetate oral tablets. Roxane Laboratories, Inc, Columbus, OH, 2009. DailyMed
  2. Product Information: CAPRELSA(R) oral tablets, vandetanib oral tablets. AstraZeneca Pharmaceuticals LP (Per Manufacturer), Wilmington, DE, 2011. DailyMed
Was this write-up helpful?
Flecainide

Keep reading about Flecainide

All Flecainide interactions (300) Flecainide drug information
Also serious with: Nirmatrelvir Mesoridazine Pimozide Mavorixafor
Vandetanib

Keep reading about Vandetanib

All Vandetanib interactions (74) Vandetanib drug information
Also serious with: Ketoconazole Topical Colchicine Ivabradine Hydroxychloroquine
Beyond drug–drug

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:

Flecainide + Activated Charcoal American Hellebore Arsenic Cesium Ephedra Grapefruit Sida Cordifolia 1,3-dmaa + 78 more
Vandetanib + Activated Charcoal American Hellebore Arsenic Cesium Ephedra Grapefruit Sida Cordifolia St. John's Wort + 138 more

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.

Coming soon

The instant two-drug checker is on its way.

In the meantime, browse the directory below to look up any drug and see its documented interactions.

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
This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.