This randomized, double-blind, placebo-controlled study will be conducted in 9 centers, study participants will be adult men with ED and insufficient response to standard therapy with 100 mg sildenafil on demand during the 4-week open label run-in-phase, follow-up in the study will be 10±2 months.~This is a standard procedure to use placebo as control in studies assessing the efficacy of pharmacological treatment of ED. Furthermore the placebo group provides a benchmark for an objective analysis of safety and tolerability findings. The open-label run-in phase assures that only subjects who are true non-responders i.e. with insufficient response to standard therapy with 100 mg sildenafil prn during the 4-week open-label run-in phase are randomized and participate in the double-blind treatment phase.~Participants distributed between groups at a ratio of 1:1.
The primary objective of this study is to investigate the efficacy of intracavernosal (Xeomin®) (100U) as add-on therapy to sildenafil 100 mg on demand in men with ED and insufficient response to standard therapy with 100 mg sildenafil on demand during the 4-week open-label run-in phase.~The secondary objectives are to further describe the efficacy and safety of (Xeomin®) 100U IC as add-on therapy to sildenafil 100 mg on demand:~to further assess efficacy using.~i) a log diary five-item questionnaire completed after each sexual attempt (Sexual Encounter Profile);~ii) a self-reporting measure that scores erection hardness on a 4 point scale completed after each sexual attempt;~iii) The Global Assessment Question.~to assess effect persistence at month 6 and month 9.~to assess safety of (Xeomin®) 100U IC in combination with sildenafil 100 mg on demand.