Efficacy of Intracavernosal as add-on Therapy to Sildenafil 100 mg on Demand Compared to Sildenafil 100 mg on Demand for the Treatment of Erectile Dysfunction (ED) Not Sufficiently Responsive to Standard Therapy With Phosphodiesterase Type 5 Inhibitors

"Administration of the investigational product.~For the double-blind treatment phase, experimental group :~Patients will receive Xeomin® (MERZ PHARMACEUTICALS GMBH), 100 U, a paired intracavernosal injection to be performed by the investigator."

"For the double-blind treatment phase, control group :~Patients will receive placebo of Xeomin® 100 U, a paired intracavernosal injection is to be performed by the investigator."