Fosamprenavir and Sildenafil interaction
Fosamprenavir and Sildenafil: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Fosamprenavir (Fosamprenavir Calcium) label · effective 2026-06-30
John’s wort ( Hypericum perforatum ) Lipid modifying agents: Lomitapide, lovastatin, simvastatin Non-nucleoside reverse transcriptase inhibitor: Delavirdine PDE5 inhibitor: Sildenafil (Revatio) (for treatment of pulmonary arterial hypertension) Sedative/hypnotics: Midazolam, triazolam Hypersensitivity to fosamprenavir calcium or amprenavir (e.g., Stevens-Johnson…
Use of PDE5 inhibitors for pulmonary arterial hypertension (PAH): •Use of sildenafil (REVATIO) is contraindicated when used for the treatment of PAH.
There is increased potential for sildenafil-associated adverse events (which include visual disturbances, hypotension, prolonged erection, and syncope) [see Contraindications (4)].
PDE5 inhibitors: Sildenafil, tadalafil, vardenafil ↑ Sildenafil ↑ Tadalafil ↑ Vardenafil May result in an increase in PDE5 inhibitor-associated adverse events, including hypotension, syncope, visual disturbances, and priapism.
Fosamprenavir calcium/ritonavir: Sildenafil: 25 mg every 48 hours.
From the Sildenafil label · effective 2026-07-17
Adverse Reactions with the Concomitant Use of Ritonavir The concomitant administration of the protease inhibitor ritonavir substantially increases serum concentrations of sildenafil (11-fold increase in AUC).
CYP3A4 inhibitors (e.g., ritonavir, ketoconazole, itraconazole, erythromycin) increase SILDENAFIL ORAL FILM exposure.
Erythromycin or strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, saquinavir): Consider a starting dose of 25 mg.
Ritonavir and other CYP3A4 inhibitors Co-administration of ritonavir, a strong CYP3A4 inhibitor, greatly increased the systemic exposure of sildenafil (11-fold increase in AUC).
Co-administration of erythromycin, a moderate CYP3A4 inhibitor, resulted in 160% and 182% increases in sildenafil Cmax and AUC, respectively.
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.