Increased blood levels & exposure w/ potent CYP3A4 inhibitors (eg, ketoconazole, itraconazole & ritonavir). Caution w/ medications metabolized by CYP3A4 hepatic enzyme isoform (eg, modern α1
-blockers), herbal remedies (St. John's wort, milk thistle) & grapefruit juice. Enhanced hypotensive effect & risk of severe postural hypotension w/ antihypertensives α-receptor blockers (prazosin, trimazosin, urapidil). Increased risk of conc & undesirable effects w/ clarithromycin, erythromycin. Risk of postural hypotension (particularly in elderly) w/ phosphodiesterase type 5 inhibitors (eg, sildenafil, tadalafil, vardenafil). Increased risk of hypotension (particularly postural) w/ nitrates, nitrites & related drugs (eg, isosorbide dinitrate, isosorbide linsidomine, molsidomine, nicorandil, nitroglycerin).