H2-receptor antagonists may be administered simultaneously with or 12 hours apart from Epclusa at a dose that does not exceed famotidine 40 mg twice daily. Coadministration of famotidine (40 mg single dose) and sofosbuvir/velpatasvir (400/100 mg single dose) was studied in 60 subjects. When given simultaneously, Cmax and AUC of sofosbuvir decreased by 8% and 18%, those of GS-331007 decreased by 16% and 6%, and those of velpatasvir decreased by 20% and 19%. When the dose of famotidine was administered 12 hours prior to sofosbuvir/velpatasvir, Cmax and AUC of sofosbuvir decreased by 23% and 20%, those of GS-331007 increased by 20% and 4%, and those of velpatasvir decreased by 13% and 15%.