 18. Concomitant use of potent Cytochrome P450 3A4 CYP3A4 inhibitors atazanavir, clarithromycin, indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin and voriconazole, grapefruit juice over 1 litre daily, CYP3A substrates with narrow therapeutic indices cyclosporine, quinidine, or inducers carbamazepine, dexamethasone, phenobarbital, phenytoin, rifampin, and rifapentine. 