Medicinal products that are potent inducers of P-gp or potent inducers of CYP2B6, CYP2C8, or CYP3A4 (e.g. rifampicin) may decrease plasma concentrations of sofosbuvir or velpatasvir leading to reduced therapeutic effect of sofosbuvir/velpatasvir. The use of such medicinal products with Epclusa is not recommended. Coadministration of rifampicin (600 mg once daily) and sofosbuvir (400 mg single dose) decreased sofosbuvir Cmax and AUC by 77% and 72%. GS-331007 Cmax increased by 23% and AUC decreased by 5%. The effect on rifampicin exposure was not studied but no change is expected. Coadministration of rifampicin (600 mg once daily) and velpatasvir (100 mg single dose) decreased velpatasvir Cmax and AUC by 71% and 82%. Coadministration of rifampicin (600 mg, single dose) and velpatasvir (100 mg, single dose) increased Cmax and AUC by 28% and 46%, respectively. The effect on rifampicin exposure was not studied but no change is expected.