Increased INR & prothrombin time w/ warfarin. May potentially interfere w/ CYP2C19 & decrease clearance of diazepam. Double exposure w/ CYP2C19 & CYP3A4 inhibitor eg, voriconazole. May increase conc of cilostazol & decrease plasma conc of atazanavir. May interfere absorption of antiretroviral drugs, ketoconazole, Fe salts & digoxin. Decreased serum levels w/ atazanavir & nelfinavir. Possible toxicity w/ saquinavir or ritonavir.