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- Original Article -
Characteristics of sildenafil erections in healthy young men
Onder Yaman1, Zafer Tokatli1, Murat Akand1, Atilla H. Elhan2, Kadri Anafarta1
1Department of Urology, 2Department of Biostatistics, University of Ankara, School of Medicine, Ankara 06100, Turkey
Abstract
Aim: To determine the effect of sildenafil citrate on the nocturnal penile erections (i.e. time to onset, the duration of
erection, and the interval between first and second erections) of healthy young men.
Methods: Twenty-two potent men, 23-29 years old, were recruited for the study. All subjects completed three sessions over consecutive nights
using the RigiScan monitoring device (Dacomed, Minneapolis, USA). After a first night of adaptation, night 2 records
were their baseline values, and on night 3 they received 100 mg of sildenafil citrate. Statistical comparisons were done
between the second and third night data.
Results: The mean time to onset of the first erection with sildenafil citrate
was (34 ± 18) min, whereas it was (74 ± 24) min
(P < 0.001) without sildenafil citrate. The number of erections
observed during the first 5 h after sildenafil citrate medication was 3.6 ± 0.5 in contrast to 2.4 ± 0.5 with no
medication (P = 0.001). The interval between first and second erections was shorter with sildenafil citrate: (52 ± 26) min
vs. (85 ± 34) min (P = 0.01). The duration of the last erection was statistically significantly longer with the sildenafil
citrate: (64 ± 33) min vs. (42 ± 28) min
(P < 0.01).
Conclusion: Healthy young men achieved erection within
34 min after sildenafil citrate administration, which is shorter than the 1 h interval proposed by the manufacturer. The
interval between the first and second erections was shorter and the duration of the last nocturnal erection was longer.
(Asian J Androl 2005 Dec; 7: 395-398)
Keywords: sildenafil citrate; nocturnal erection; nocturnal penile tumescence; rigidity testing; erectile dysfunction
Correspondence to: Dr Onder Yaman, Sehit Ersan Cad., Pembe
Kösk Sitesi, B-1 Blok, No 15, 06680, Çankaya, Ankara, Turkey.
Tel: +90-312-427-69-71 Fax: +90-312-311-21-67
E-mail: yaman@medicine.ankara.edu.tr
Received 2004-09-27 Accepted 2005-05-08
DOI: 10.1111/j.1745-7262.2005.00053.x
1 Introduction
The introduction of sildenafil citrate, the first
effective oral agent for erectile dysfunction (ED), has led to
major changes in ED management and widespread use of this medication worldwide [1-4]. More than 20
million patients have been treated with sildenafil citrate for
ED [5, 6]. Therefore, sildenafil is one of the most widely
studied drugs effective in ED [7-9].
Although pharmacokinetic parameters of sildenafil
were well established in previous studies, the aim of our
study was to observe the effect of the drug on nocturnal
penile tumescence and rigidity (NPTR) (time to onset,
duration of erection and the interval between the first
and second erections) in healthy young male volunteers.
2 Materials and methods
2.1 Patients
Twenty-two medical students (n = 8) and urology
residents (n = 14), 23-29 years old at University of
Ankara, Turkey, were recruited for the study. A
disorder-free medical and sexual history and normal erectile
function were recorded.
2.2 Study protocol
According to the study protocol, changes in NPTR
of the subjects¡¯ penises were determined at home for the
3 consecutive nights using the RigiScan monitoring
device (Dacomed, Minneapolis, USA).
During the first night which was considered as
adaptation night (night 1), the RigiScan monitoring device
was applied to the penis and turned off; participants were
then studied for further 2 nights, which involved the
record of penile erectile activity. The night 2 records
were treated as baseline values, while on night 3, they
received 100 mg of sildenafil (Pfizer, New York, NJ,
USA). Participants were invited to go to bed at their
usual time, at least 2 h after the end of a meal without the
intake of any alcohol- or caffeine-containing beverages
as well as any kind of medication.
2.3 Data analysis
After each monitoring period, all data were
transferred to a personal computer. At the end of the study,
data were analyzed with RigiScan Plus software version
4.0. The software recognized erectile activity as a 20 %
increase in the base loop circumference that persisted
for at least 3 min. It also calculated units of tumescence
and rigidity each night separately. Sessions lasting for
less than 5 h were excluded from further analysis. The
correlation between duration and erectile activity during
sleep was measured by determining the following parameters: number of erection during the first 5 h (with
tip rigidity greater than 60 % and duration greater than
10 min), time to onset of first erection, interval between
the first and second erections and duration of last erection.
2.4 Statistical analysis
Data were expressed in mean ± SD if applicable.
Paired t-test and Wilcoxon signed ranks test were used
as appropriate. P < 0.05 was considered significant.
3 Results
All 22 subjects completed the study protocol and no
session was less than 6 h in duration. The average
duration of sleep was 7 h. We only observed transient
headache in one subject as a side-effect of sildenafil.
The mean time for onset of erection with sildenafil
citrate was (34 ± 18) min but (74 ± 24) min without
sildenafil citrate (P < 0.001). The number of erections
observed during the first 5 h after the administration of
sildenafil citrate medication was 3.6 ± 0.5 in contrast to
2.4 ± 0.5 with no medication
(P = 0.001). The interval between the first and second erections was shorter when
sildenafil citrate was administered: (85
± 34) min vs.
(52 ± 26) min (P = 0.01).
The duration of the last erection was significantly longer with sildenafil citrate:
(64 ± 33) min vs. (42 ± 28) min
(P < 0.01) (Table 1).
4 Discussion
Previous studies have shown that following oral
administration, sildenafil absorption occured rapidly, with
maximum plasma concentrations (Cmax) occuring within
1 h (30 min-120 min in fasted state) [10-12]. The
ingestion of high-fat meals delays the absorption by
40 min-65 min probably because of delayed gastric emptying
[13]. Hence most studies evaluated the efficacy of
sildenafil directed patients to take sildenafil approximately
1 h before sexual activity, and it was commonly thought
by the patients that sildenafil takes at least 1 h to
work [14]. However, Padma-Nathan et al. [15] showed that the time
to onset of erection induced by sildenafil was as brief as
14 min after dosing, and most of the men with ED who
took sildenafil were able to achieve at least one erection
that resulted in successful intercourse within 20 min
(51 %) or 30 min (68 %). Overall, the median time to
onset of an erection after taking sildenafil that resulted in
successful intercourse was 36 min.
Although there was a wealth of conventional
information on pharmacokinetics and pharmacodynamics of
sildenafil on patients with ED, there has not been much
published in the area of young healthy volunteers using
occasional sildenafil. In our study when we analyzed
our NPTR data, we calculated that the mean time to
onset of erection with sildenafil was 34 min; however, it
was 74 min on night 2 (without sildenafil). Our result
of 34 min was slightly longer than Eardly¡¯s findings
(27 min) [11].
However, Eardly¡¯s study [11] was different from
ours as results were determined by the RigiScan
monitoring device following visual sexual stimulation after
different dosages (50 mg vs. 100 mg) of sildenafil citrate
were administered.
It has been suggested that erections occurring
during rapid eye movement(REM) sleep were initiated by
the release of nitric oxide from
nonadrenergic-noncho-linergic nerves that then activated the hemodynamic
cascade of events leading to rigidity [16]. As a contrast to
the classical knowledge about sildenafil that it worked at
patients with ED, we observed significant improvement
in the nocturnal erections of healthy young men without
ED and without sexual stimulation after sildenafil
administration [17]. Since sildenafil used the same cascade of
erection physiology, this could explain the night time
effect of sidenafil. In fact there was no sexual stimulation
during nocturnal penile erections, but the other steps to
erection were same.
In our study we also observed that the number of
erections observed during the first 5 h after sildenafil
medication was significantly more than without
medication (n = 3.6 vs.
n = 2.4, P = 0.001). And also the
interval between the first and second erections was shorter
on the nights when sildenafil was administered (85 min
vs. 52 min, P = 0.01). This observation was supported
by Mondaini et al. [18], who stated that sildenafil
reduced the postorgasmic refractory time (although the
postorgasmic refractory period was linked to hormonal,
and neurohormonal factors related to orgasm and not
just to the occurrence of an erection). However, in contrast to our previous study[17], Mondaini
et al. [18] also stated that sildenafil did not improve erections in healthy
young men. We knew that our study was preliminary
and a more rigorous, double-blinded, placebo-controlled,
randomized trial was required, perhaps even one in a sleep
laboratory setting where sleep architecture can be
examined.
In conclusion, our NPTR data showed that healthy
young men achieve erection within 34 min of taking
sildenafil, which is shorter than the generally accepted
1 h interval. Secondly, sildenafil might reduce the length
of time between the first and second nocturnal erections,
which implies that it is a potential therapeutic for
different sexual disorders.
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