Based on theoretical considerations darunavir/cobicistat is expected to increase tadalafil plasma concentrations (CYP3A inhibition). Co-administration of tadalafil for the treatment of pulmonary arterial hypertension with darunavir/cobicistat is not recommended.

Coadministration is expected to increase concentrations of tadalafil. 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. The following dose adjustments are recommended for use of tadalafil with darunavir/cobicistat. Initiation of tadalafil in patients taking darunavir/cobicistat: in patients receiving darunavir/cobicistat for at least one week, start tadalafil at 20 mg once daily. Increase to 40 mg once daily based upon individual tolerability. Initiation of darunavir/cobicistat in patients taking tadalafil: avoid use of tadalafil during the initiation of darunavir/cobicistat. Stop tadalafil at least 24 hours prior to starting darunavir/cobicistat. After at least one week following the initiation of darunavir/cobicistat, resume tadalafil at 20 mg once daily. Increase to 40 mg once daily based upon individual tolerability. Patients switching from darunavir co-administered with ritonavir to darunavir/cobicistat: maintain tadalafil dose.