Methods: We conducted a randomized, double-blind, crossover study consisting of four treatment arms. Because the dosing instructions for sildenafil and tadalafil are different, a unique methodology using sham placebo arms was employed to maintain the blind. To assess drug preference, 219 patients were randomized to either sildenafil 50 mg or tadalafil 20 mg, with dosing instructions reflecting their respective product profiles. To assess dosing instruction preference during tadalafil therapy, 46 patients were randomized to tadalafil 20 mg with either tadalafil or sildenafil dosing instructions. After 12 weeks, patients were crossed-over. After 4 weeks of each treatment, all patients following sildenafil dosing instructions were offered the opportunity for an upward dose titration. In a double-blind fashion, all patients who requested an upward titration received additional capsules. To mimic the pattern of dose usage observed in clinical practice, the number of patients who received additional double-blind active medication was limited to 35% of patients taking sildenafil in each treatment period in each country. Following the crossover treatment period, patients chose their preferred double-blind treatment with dosing instructions to receive in the 12-week extension period.

Results: In the drug preference assessment, 132 of 181 (73%) evaluable patients chose to receive tadalafil (p < 0.001) during the extension period. In the dosing instruction preference assessment, 24 of 36 (67%) evaluable patients preferred tadalafil with tadalafil dosing instructions (p = 0.046). Sildenafil and tadalafil were well tolerated.

Conclusions: In the doses utilized in this study, 73% of patients preferred tadalafil with tadalafil dosing instructions for the treatment of their erectile dysfunction over sildenafil with sildenafil dosing instructions. During tadalafil therapy, 67% of patients preferred tadalafil dosing instructions over sildenafil dosing instructions. (C) 2004 Elsevier B.V. All rights reserved.