Conflict of Interest. Dr. Saikali is an employee of ICOS. Drs. Watkins and Pullman are employees of Lilly.
Introduction. Tadalafil is a phosphodiesterase 5 (PDE5) inhibitor used for the treatment of erectile dysfunction (ED). The minimal time to onset of erectogenic effect in the at-home setting has not been evaluated.
Aim. The goal was to determine the earliest time to erectogenic effect leading to successful intercourse within 30 minutes after taking tadalafil 10 and 20 mg.
Methods. The multicenter, randomized, double-blind, placebo-controlled, parallel-group, phase-2 study enrolled men at least 21 years old with a minimum 3-month history of ED. Four single doses each of placebo, tadalafil 10 mg, or 20 mg were taken at home once every 8–10 days. Using a stopwatch, couples recorded in Sexual Encounter Profile diaries the earliest time within 30 minutes after dosing to the first erection adequate for vaginal penetration, and whether the erection led to successful intercourse.
Main Outcome Measures. The primary analysis compared the percentage of erections resulting in successful intercourse between tadalafil groups and placebo at one-minute intervals using a step-down procedure. A secondary analysis compared the overall distribution of time to erectogenic effect between treatment groups using the Cox Regression Method.
Results. Compared to placebo, a significant erectogenic response to tadalafil 20 mg was found from 30 minutes down to 16 minutes after dosing (P = 0.012). Response to tadalafil 10 mg approached significance (P = 0.054) at 30 minutes. As analysed by the Cox Regression Method, a significant erectogenic response was found from 30 minutes down to 15 minutes after dosing for tadalafil 20 mg (P = 0.020), and from 30 minutes down to 26 minutes for tadalafil 10 mg (P = 0.042). Fifty-two percent of men taking tadalafil 20 mg had at least one successful intercourse attempt within 30 minutes compared to 35.1% of men taking placebo (P = 0.038).
Conclusions. This stopwatch-based study demonstrated a pharmacodynamic effect within 30 minutes after dosing for tadalafil 10 and 20 mg.