Allergy to sulfa. Risk of syncope. Evaluate for the presence of carcinoma of the prostate prior to start of therapy. Intraoperative floppy iris syndrome during cataract surgery. Do not use in combination w/ strong CYP3A4 inhibitors (eg, ketoconazole), strong CYP2D6 inhibitors (eg, paroxetine) & other α-adrenergic blocking agents. Caution in concomitant w/ cimetidine & warfarin. Priapism. May affect ability to drive or operate machinery. Not indicated for use in women & childn.