- receiving concurrent medications that may either bind to or are a substrate for CYP 450 2D6 or inhibit/induce CYP 3A3/4 activity. These include: anti-HIV medications, azole antifungal medications, calcium channel antagonists, carbamazepine, cimetidine, macrolide antibiotics (erythromycin, clarithromycin), phenytoin, propoxyphene, rifampin, or tramadol.