Drug interactions
Fosamprenavir + Tadalafil
Severity: Major
Fosamprenavir and Tadalafil: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Fosamprenavir (as amprenavir, boosted or not) inhibits CYP3A4 and increases tadalafil exposure. This can cause marked hypotension, syncope, visual changes and prolonged erection.
What this interaction means in plain words
Fosamprenavir and Tadalafil can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Amprenavir inhibits CYP3A4, reducing tadalafil clearance and increasing exposure.
What to do
For erectile dysfunction, cap tadalafil at the reduced doses in labeling and monitor for hypotension and priapism. For pulmonary hypertension, follow labeling for stopping and restarting tadalafil at a low dose around protease inhibitor initiation.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Tadalafil
- Amyl nitrite + Tadalafil Contraindicated
- Isosorbide dinitrate + Tadalafil Contraindicated
- Isosorbide mononitrate + Tadalafil Contraindicated
- Nitroglycerin po + Tadalafil Contraindicated
- Nitroglycerin rectal + Tadalafil Contraindicated
- Nitroglycerin sublingual + Tadalafil Contraindicated
Frequently asked questions
Can I take Fosamprenavir with Tadalafil?
MediHelp rates the interaction as major. Fosamprenavir and Tadalafil can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Fosamprenavir (as amprenavir, boosted or not) inhibits CYP3A4 and increases tadalafil exposure. This can cause marked hypotension, syncope, visual changes and prolonged erection.
How serious is the interaction between Fosamprenavir and Tadalafil?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: For erectile dysfunction, cap tadalafil at the reduced doses in labeling and monitor for hypotension and priapism. For pulmonary hypertension, follow labeling for stopping and restarting tadalafil at a low dose around protease inhibitor initiation.
What other medicines interact with Tadalafil?
MediHelp also lists interactions of Tadalafil with, for example, Amyl nitrite, Isosorbide dinitrate, Isosorbide mononitrate. The full list is on the Tadalafil page.
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