Drug interactions
Fosamprenavir + Sildenafil
Severity: Major
Fosamprenavir and Sildenafil: 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
Amprenavir, the active metabolite of fosamprenavir, inhibits CYP3A4 and can substantially raise sildenafil concentrations. This increases the risk of hypotension, syncope, visual disturbance and prolonged erection.
What this interaction means in plain words
Fosamprenavir and Sildenafil 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
CYP3A4 inhibition by amprenavir decreases sildenafil clearance.
What to do
For erectile dysfunction, limit sildenafil to a 25 mg dose no more than once every 48 hours. For pulmonary hypertension, avoid or use only with close blood pressure monitoring.
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 Sildenafil
- Amyl nitrite + Sildenafil Contraindicated
- Atazanavir + Sildenafil Contraindicated
- Cobicistat + Sildenafil Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Sildenafil Contraindicated
- Glyceryl trinitrate pr + Sildenafil Contraindicated
- Isosorbide dinitrate + Sildenafil Contraindicated
Frequently asked questions
Can I take Fosamprenavir with Sildenafil?
MediHelp rates the interaction as major. Fosamprenavir and Sildenafil 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. Amprenavir, the active metabolite of fosamprenavir, inhibits CYP3A4 and can substantially raise sildenafil concentrations. This increases the risk of hypotension, syncope, visual disturbance and prolonged erection.
How serious is the interaction between Fosamprenavir and Sildenafil?
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, limit sildenafil to a 25 mg dose no more than once every 48 hours. For pulmonary hypertension, avoid or use only with close blood pressure monitoring.
What other medicines interact with Sildenafil?
MediHelp also lists interactions of Sildenafil with, for example, Amyl nitrite, Atazanavir, Cobicistat. The full list is on the Sildenafil page.
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