© The Canadian Journal of Urology™; 19(Supplement 1); October 2012
GREENSPAN AND BARKIN
20
TABLE 1.
Oral phosphodiesterase-5 (PDE-5) inhibitors for erectile dysfunction (ED)
Name
Dose
Time to maximum
Serum
Affected
Side effects/Notes*
(
Brand name)
plasma concentration half life
by food
Sildenafil
25
mg-100 mg
60
minutes
4
hrs
Yes;
Visual disturbances
(
Viagra)
30-60
minutes
delays
(“
blue haze”)
before sexual activity,
onset
Max 1x day
Vardenafil
5
mg-20 mg
60
minutes
4
hrs
Yes;
Increases QT interval;
(
Levitra)
25-60
minutes
delays
avoid use with other
before sexual activity
onset
medications which
Max 1x day
have similar side effect
Vardenafil
10
mg oral disintegrating 60 minutes
4
hrs
Yes;
Same as Levitra
(
Staxyn)
tablet (ODT) 45-90
delays
minutes before
onset
sexual activity.
Absorbed on the
tongue (not under)
without water
Tadalafil
10
mg-20 mg
120
minutes
17.5
hrs
No
Myalgia, back pain
(
Cialis)
30
min before
sexual activity
Max 1x day
Daily dosing:
2.5
mg-5 mg daily
Avanafil
100
mg
30
minutes
3
hrs
No
Back pain
(
Stendra
(50
mg-200 mg)
[
US only])
30
minutes before
sexual activity
Max 1x day
*
Class side effects include: headache, flushing, rhinitis, dyspepsia
•
Inadequate dose of ED therapy: maximal dosages
should and can be used safely to initiate therapy
•
Inadequate patient arousal or stimulation
•
Inadequate timing between therapy and attempted
intercourse
•
Not enough trials with a particular ED agent: four
attempts with one agent may be needed
•
The effect of ED therapy may be outweighed by
multiple factors that affect erections, such as stress,
fatigue, alcohol, smoking, obesity, diabetes, and
vascular insufficiency
•
Wrong diagnosis: the patient may have primary
PME as opposed to ED
•
Low testosterone levels: in a recent trial,
14
in 162
patients treated with a PDE-5 inhibitor, the odds
ratio for lack of response to a PDE-5 inhibitor in
patients with hypogonadism versus patients with
normal testosterone levels was 1.89 (p = 0.0012).
PDE-5 inhibitors and nitrates:
Patients using a PDE-
5
inhibitor should never take a nitrate. The duration
of action of a PDE-5 inhibitor (hours versus days) is
irrelevant, if intercourse activity may produce angina
that may require nitroglycerin in any form (pill, patch,
spray, or sublingual). Studies have shown that in 8%of
men, the combination of a nitrate and a PDE-5 inhibitor
can cause a precipitous drop in blood pressure, asmuch
as 40 mmHg, which could cause sudden cardiac death
or other signs of vascular insufficiency. The problem
is that we cannot predict which men will be in the 8%
that experience this effect, so the contraindication is
firm and the same for all of the PDE-5 inhibitors.
15-17
Counterfeiting of PDE-5 inhibitors:
A discussion of
PDE-5 inhibitors should not ignore the rampant
counterfeit market and its potential dangers.
18
There
are several reports of “natural therapies” that contain
unlabelled quantities of PDE-5 inhibitors. This is a
