Based on theoretical considerations darunavir/cobicistat is expected to increase sildenafil plasma concentrations (CYP3A inhibition). Concomitant use of sildenafil for the treatment of erectile dysfunction with darunavir/cobicistat should be done with caution. If concomitant use of darunavir/cobicistat with sildenafil is indicated, sildenafil at a single dose not exceeding 25 mg in 48 hours is recommended.

Coadministration is expected to increase concentrations of sildenafil. Co-administration with PDE-5 inhibitors may result in an increase in PDE-5 inhibitor-associated adverse reactions including hypotension, syncope, visual disturbances and priapism. Sildenafil at a single dose not exceeding 25 mg in 48 hours can be used with increased monitoring for PDE-5 inhibitor-associated adverse reactions.