• erectile dysfunction;
  • sildenafil citrate;
  • duration of action;
  • onset of action

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

Methods  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® 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.

Results 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).

Conclusions  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.