title: Onset and duration of action of sildenafil for the treatment of erectile dysfunction.
abstract: OBJECTIVE
  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(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.
  
  
  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.
authors.affiliation: Department of Urology, St James University Hospital, Leeds, West Yorkshire and Pfizer Ltd, Sandwich, Kent, UK.
authors.forename: Ian
authors.initials: I
authors.lastname: Eardley
authors.forename: Peter
authors.initials: P
authors.lastname: Ellis
authors.forename: Mitradev
authors.initials: M
authors.lastname: Boolell
authors.forename: Maria
authors.initials: M
authors.lastname: Wulff
mesh_terms: D000328:Adult; D017668:Age of Onset; D000368:Aged; D018592:Cross-Over Studies; D004311:Double-Blind Method; D006801:Humans; D018783:Impotence, Vasculogenic / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D010726:Phosphodiesterase Inhibitors / Q000627:therapeutic use*; D010879:Piperazines / Q000627:therapeutic use*; D011687:Purines; D000068677:Sildenafil Citrate; D013450:Sulfones; D013997:Time Factors; D016896:Treatment Outcome; D014665:Vasodilator Agents / Q000627:therapeutic use*
chemical_list: D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014665:Vasodilator Agents; D000068677:Sildenafil Citrate