Onset and duration of action of sildenafil for the treatment of erectile dysfunction

To determine the onset and duration of action of sildenafil in patients with erectile dysfunction (ED).

Two randomised, double-blind, placebo-controlled, two-way crossover studies were conducted in men with ED of no known organic cause. Study I: The time to onset of erections after sildenafil (50 mg) or placebo dosing following visual sexual stimulation (VSS) was assessed in 17 patients. Patients not achieving >60% penile rigidity by 70 min postdose as measured by a RigiScan(R) monitoring device were assigned an onset time of 70 min. Study II: The duration of grade 3 (hard enough for penetration) and grade 4 (fully hard) erections, determined by self-assessment during 60 min of VSS starting 2 and 4 h after sildenafil (100 mg) or placebo dosing, was measured in 16 patients.

Study I: The median time (range) to onset of erections was 27 min (in a range of 12--70) after receiving sildenafil 50 mg. In the sildenafil group, 71% of patients experienced onset of erections within 30 min of dosing, and 82% responded within 45 min. Of the patients who achieved >60% penile rigidity after sildenafil, 86% had done so by 30 min after dosing. Study II: When VSS began 2 h postdose, the median duration of grade 3 or 4 erections was 19.5 min (0--55) for sildenafil vs 0 min (0--23) for placebo. When VSS began 4 h postdose, the median duration was 5 min (0--45) for sildenafil compared with 0 min for placebo (0--27).

Sildenafil is an effective oral treatment for ED that produces a penetrative erection as early as 12 min and for most patients, within 30 min after dosing, and a duration of action lasting at least 4 h.