Coadministration has not been studied. Solifenacin is metabolized by CYP3A4 and concentrations are likely to increase due to inhibition of CYP3A4. A 3-fold increase in solifenacin exposure was observed with ketoconazole (a strong inhibitor of CYP3A4). It is recommended that solifenacin dosage should be limited to 5 mg once daily if coadministered with a strong CYP3A4 inhibitor such as darunavir/cobicistat. Emtricitabine and tenofovir alafenamide do not interfere with this metabolic pathway.