Increased susceptibility to vasodilators including left ventricular outflow obstruction (eg, aortic stenosis, hypertrophic obstructive cardiomyopathy) or rare syndrome of multiple system atrophy manifesting as severely impaired autonomic BP control. Serious CV events including MI, unstable angina, sudden cardiac death, ventricular arrhythmia, cerebrovascular hemorrhage, transient ischemic attack, HTN & hypotension. Anatomical penis deformation (eg, angulation, cavernosal fibrosis or Peyronie's disease) or hematological disorders predisposing to priapism (eg, sickle cell anemia, multiple myeloma or leukemia). Discontinue if sudden visual/hearing defect occurs. Co-administration w/ α-blocker. In vitro
potentiation of Na nitroprusside antiaggregatory effect. Hepatic or severe renal impairment. May affect ability to drive or operate machinery.