To investigate the efficacy and safety of tadalafil, a phosphodiesterase type 5 inhibitor, in Japanese men with erectile dysfunction (ED).

This multicenter, randomized, double-blind, placebo-controlled, 12-week study enrolled 343 Japanese men with ED. The men were stratified into those with mild, moderate, or severe ED and then randomly assigned 1:1:1:1 to placebo and 5 mg, 10 mg, and 20 mg tadalafil. Co-primary outcomes were the International Index of Erectile Function erectile function domain score, the percentage of “yes” responses to the Sexual Encounter Profile Diary Questions 2 and 3, and tolerability. Secondary outcomes included the International Index of Erectile Function intercourse satisfaction and overall satisfaction domain scores and the percentage of “yes” responses to a global assessment question.

The least square mean change from baseline was 7.5, 9.1, and 9.4 for 5, 10, and 20 mg tadalafil versus 2.1 for placebo for the International Index of Erectile Function erectile function domain; 28.5, 36.0, and 36.5 for 5, 10, and 20 mg tadalafil versus 8.6 for placebo for Sexual Encounter Profile question 2; and 34.3, 47.3, and 50.8 for 5, 10, and 20 mg tadalafil versus 12.3 for placebo for Sexual Encounter Profile question 3, respectively (P <0.001 for all doses and all measures). Patients taking tadalafil had significantly greater changes from baseline for the intercourse satisfaction and overall satisfaction domains compared with patients taking placebo (P <0.001). Also, 76.5%, 81.4%, and 83.7% of patients taking 5, 10, and 20 mg tadalafil, respectively, reported improved erections (global assessment question) versus 31.4% of patients taking placebo (P <0.001). Most (98%) treatment-emergent adverse events were mild or moderate in severity. One patient (tadalafil 5 mg) discontinued because of an adverse event (ureteral calculus). Of the 343 patients, 302 (88%) completed the study. No deaths were reported.

All doses of tadalafil studied were efficacious and well tolerated in Japanese men with ED.