Consider patient's CV status. Discontinue in case of sudden visual defect. Severe renal & hepatic insufficiency. Priapism-predisposing conditions (eg, sickle cell anaemia, multiple myeloma, leukaemia). Anatomical deformation of the penis. Hereditary problems of galactose intolerance, Lapp lactase deficiency, glucose-galactose malabsorption. Concomitant α-blockers, guanylate cyclase stimulators, potent CYP3A4 inhibitors. Childn & adolescent <18 yr.