Flecainide and Saquinavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Saquinavir
No brand names on recordFlecainide
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 flecainide plasma concentrations and increased risk for serious cardiac arrhythmia
Interaction Deep Dive
Flecainide and saquinavir are both CYP3A substrates and are associated with QT interval prolongation21. Additionally, ritonavir-boosted saquinavir is a potent CYP3A inhibitor. Using these agents together may increase the exposure of flecainide, with the potential for serious and/or life-threatening cardiac arrhythmia. Therefore, the concomitant use of flecainide and ritonavir-boosted saquinavir is contraindicated 2.
Why it happens (mechanism)
Inhibition of CYP3A-mediated flecainide metabolism by saquinavir; additive effects on QT prolongation
Common questions
Can I take Flecainide and Saquinavir together?
Increased flecainide plasma concentrations and increased risk for serious cardiac arrhythmia Always confirm with your pharmacist or prescriber before making any change.
How serious is the Flecainide and Saquinavir interaction?
It is rated contraindicated. These should generally not be used together.
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 "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 Flecainide or Saquinavir 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)
- Product Information: flecainide acetate oral tablets, flecainide acetate oral tablets. Roxane Laboratories, Inc, Columbus, OH, 2009. DailyMed
- Product Information: INVIRASE(R) oral capsules, tablets, saquinavir mesylate oral capsules, tablets. Genentech USA, Inc. South San Francisco, CA, 2010. DailyMed
Keep reading about Saquinavir
Keep reading about Flecainide
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