- Subjects with Contraindications to PDE5i therapy. Namely patients receiving treatment with nitrate based medication or patients that for various reasons cannot take PDE5 inhibitors (severe hepatic diseases- cirrhosis or ALT (Alanine aminotransferase)>2x upper limit of normal), renal impairment (creatinine clearance > 30ml/min) or known hereditary degenerative retinal disorders such as retinitis pigmentosa. ,