Hypersensitivity. Co-administration w/ nitrates or nitric oxide donors eg, amyl nitrite. Patients who have loss of vision in 1 eye because of non-arteritic anterior ischemic optic neuropathy. Men for whom sexual activity is inadvisable (eg, patients w/ severe CV disorders). Severe hepatic impairment (Child-Pugh C), end-stage renal disease requiring dialysis, hypotension (BP <90/50 mmHg), recent history of stroke or MI (w/in the last 6 mth), unstable angina, known hereditary retinal degenerative disorders eg, retinitis pigmentosa. Concomitant use w/ ketoconazole & itraconazole (oral form) in men >75 yr; HIV PIs eg, ritonavir & indinavir; guanylate cyclase stimulators eg, riociguat.