BACKGROUND: Empiric observation suggests that the period of effectiveness of sildenafil may be longer than its half-life of 4 hours. We sought to better define the period of responsiveness to sildenafil in 2 double-blind, placebo-controlled (DBPC) trials.
METHODS: Study 1 had a crossover design with two 4-week DBPC phases, whereas study 2 included a single 4-week DBPC phase. In both studies, men with mild to moderate ED (6-question International Index of Erectile Function Erectile Function domain score of 11−25) were given sildenafil (100 mg) or placebo and asked to have sexual intercourse 8h postdose (7−9h) during an initial 4-week phase. In the first study, men crossed over to the other medication and were asked to have sexual intercourse 12h postdose (11−13h) in a second 4-week phase. The primary endpoint was the mean per-patient proportion of occasions (PPP) of “yes” responses to question 3 of the Sexual Encounter Profile (SEP Q3), “Did your erection last long enough for you to have successful intercourse?” Other endpoints were the mean PPP of occasions of erection hardness score (EHS) of 1 to 4 and percentage of men satisfied with treatment (Erectile Dysfunction Inventory of Treatment Satisfaction [EDITS] Index >50).
RESULTS: A total of 351 men were randomized in the first study, and significant efficacy over placebo was demonstrated with sildenafil at both 8 and 12 hours postdose (table). In the second study, 250 men were randomized to placebo (n=124; mean age±SD=52.9±9.0y) or sildenafil (n=126; mean age±SD=52.3±8.8y), and similarly significant efficacy over placebo was demonstrated with sildenafil at 8 hours postdose (table).
CONCLUSIONS: These findings illustrate that the period of responsiveness after a single dose of sildenafil in men with mild to moderate ED may be much longer than the 4 hours currently thought by many clinicians and patients to be the effective time period of sildenafil.

		Study 1			Study 2
		Mean ±SD	Mean (95%CI)*	Mean (95%CI)*	Mean ±SD	Mean (95%CI)*
		Baseline	8h	12h	Baseline	8h
SEPQ3	P	42±38	50 (43−57)	52 (44-60)	45±39	43 (36-51)
(PPP%)	S	48±39	76 (69-82)	79 (72−85)	39±37	85 (80-89)
EHS 4	P	_	10 (7−15)	17 (12−23)	_	7 (4−11)
(PPP%)	S	_	41 (34−48)	44 (37−51)	_	43 (36−50)
EDITS	P	_	37 (30−45)	54 (45−62)	_	29 (21−38)
(% satisfied)	S	_	84 (77−89)	77 (70−83)	_	86 (78−91)
*P<0.0001 for odds ratio for end-of-treatment score for sildenafil (S) vs placebo (P). CI=confidence interval; SD=standard deviation.