Daily Tadalafil 5 mg Combined With On-Demand Sildenafil 100 mg for Treatment of Erectile Dysfunction in PDE-5I Non Responder Patients

The goal of this clinical trial is to evaluate whether daily dosing with tadalafil 5 mg combined with on-demand sildenafil 100 mg can improve erectile function in men with erectile dysfunction (ED) who do not respond to PDE5 inhibitor alone. The main questions it aims to answer are: * Does the combination of daily tadalafil and on-demand sildenafil lead to a greater improvement in erectile function (measured by the IIEF-EF domain) compared with on-demand sildenafil alone? * Is the combination therapy safe and well tolerated in this patient population? Researchers will compare: * Group A: Daily tadalafil 5 mg plus on-demand sildenafil 100 mg * Group B: Daily placebo plus on-demand sildenafil 100 mg to determine whether the combination regimen provides superior improvement in erectile function and patient satisfaction. Participants will: * Undergo baseline assessment including medical history, physical examination, and laboratory tests. * Be randomly assigned to one of the two treatment groups. * Take the assigned medications for 12 weeks. * Complete follow-up evaluations at 4, 8, and 12 weeks, including: International Index of Erectile Function (IIEF-15) questionnaire Erection Hardness Score (EHS) assessment Reporting of any adverse effects