Coadministration has not been studied. Silodosin is a substrate of CYP3A4 and P-gp and coadministration is expected to increase silodosin concentrations. Coadministration of silodosin (8 mg single dose) and ketoconazole (400 mg, a strong CYP3A4 inhibitor), increased silodosin Cmax and AUC by 3.8-fold and 3.2-fold. The US product label for silodosin contraindicates coadministration with strong CYP3A4 inhibitors (such as darunavir/cobicistat). However, given its uroselective effect and wide therapeutic index, silodosin may be used at 4 mg with caution and monitoring for toxicity. No interactions are expected with emtricitabine and tenofovir alafenamide.