Conc may be increased by CYP3A4 (ketoconazole, itraconazole, macrolides eg, erythromycin) & CYP2C9 inhibitors, & decreased by CYP3A4 & CYP2C9 inducers (eg, carbamazepine, phenytoin, phenobarb). Decreased BP, postural dizziness & orthostatic hypotension may occur w/ alcohol. May cause decreased BP w/ α-blockers (doxazosin, terazosin), amlodipine. Decreased AUC & Cmax
w/ bosentan. Increased plasma conc w/ cimetidine, PIs (eg, ritonavir, indinavir, saquinavir), serotonin reuptake inhibitors (eg, fluvoxamine), tacrolimus. Increased plasma levels w/ ciprofloxacin, delavirdine. May potentiate vasodilatory effect of circulating nitric oxide; nitrates (eg, isosorbide dinitrate, isosorbide mononitrate, nitroglycerin). Increased clearance w/ rifampin & other CYP3A4 inducers. Increased incidence of bleeding w/ anticoagulants (vit K dependent). Increased serum levels/toxicity w/ grapefruit juice. Decreased levels w/ St. John's wort.