Avanafil and Fosamprenavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Fosamprenavir
Avanafil
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 avanafil clearance and increased avanafil plasma concentrations
Interaction Deep Dive
Concomitant use of avanafil, a CYP3A4 substrate, and fosamprenavir, a moderate CYP3A4 inhibitor, may result in increased plasma concentrations of avanafil. Although coadministration of avanafil and fosamprenavir has not been studied, avanafil Cmax and AUC increased 2-fold and 3.6-fold, respectively, when a single 200-mg dose of avanafil was coadministered with erythromycin 500 mg twice daily (also a moderate CYP3A4 inhibitor) in a study of 15 healthy volunteers. Avanafil doses should not exceed 50 mg once every 24 hours in patients taking fosamprenavir1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated avanafil metabolism by fosamprenavir
Common questions
Can I take Avanafil and Fosamprenavir together?
Decreased avanafil clearance and increased avanafil plasma concentrations Always confirm with your pharmacist or prescriber before making any change.
How serious is the Avanafil and Fosamprenavir interaction?
It is rated moderate. Can be significant — usually manageable with 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 Avanafil or Fosamprenavir 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 anything you'd monitor while I'm on both?
References (1)
- Product Information: STENDRA(TM) oral tablets, avanafil oral tablets. Vivus, Inc. (per Manufacturer), Mountain View, CA, 2012. DailyMed
Keep reading about Fosamprenavir
Keep reading about Avanafil
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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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