4. Concomitant use of MDR and CYP3A modulating drugs such as Ca+-entry blockers (verapamil, dihydropyridines), cyclosporine, quinidine, quinine, tamoxifen, megestrol and grapefruit juice, concomitant use of HIV medications; other protease inhibitors,(non) nucleoside analoga, St. Johns wort or macrolide antibiotics as erythromycin and clarithromycin.