Co-administration w/ nitrates or nitric acid donors. Men w/ severe CV disorders for whom sexual activity is inadvisable. Concomitant use w/ CYP3A4 inhibitors [ritonavir, indinavir, ketoconazole & itraconazole (oral)] in men >75 yr. Severe hepatic impairment, endstage renal disease requiring dialysis. Unstable angina. Known degenerative retinal disorders eg, retinitis pigmentosa. Patients w/ anatomical deformation of the penis or conditions predisposing to priapism.