Medications and Drugs
GENERIC NAME: sildenafil
BRAND NAME: Viagra, Revatio
DRUG CLASS AND MECHANISM: It has been estimated that
impotence
affects 140 million men worldwide. Over half of all men with
impotence are
thought to have some physical (medical) cause. The remainder
are believed
to have psychogenic causes of impotence. Medical causes of
impotence
include diabetes and circulatory, neurological or urological
conditions.
Penile erection is caused by the engorgement of the penis with
blood.
This engorgement occurs when the blood vessels delivering blood
to the
penis increase the delivery of blood and the blood vessels
carrying blood
away from the penis decrease the removal of blood. Under normal
conditions, sexual stimulation leads to the production and
release of
nitric oxide in the penis. Nitric oxide then activates the
enzyme,
guanylate cyclase, which causes the production of cyclic
guanosine
monophosphate (cGMP). It is the cGMP that is primarily
responsible for the
erection by affecting the amount of blood that the blood
vessels deliver
and remove from the penis.
Sildenafil also reduces the pressure in the pulmonary artery in a serious
condition called pulmonary arterial hypertension.
Sildenafil inhibits an enzyme called phosphodiesterase-5
(PDE5) which
destroys the cGMP. Thus, sildenafil prevents the destruction of
cGMP and
allows cGMP to accumulate and persist longer. The longer cGMP
persists,
the more prolonged the engorgement of the penis.
PRESCRIPTION: Yes
GENERIC AVAILABLE: No
PREPARATIONS: Viagra is a
blue, film-coated, rounded, diamond-shaped tablets that comes in 25, 50, and 100
mg tablets for treating impotence. Revatio comes in a 20 mg tablet
and
is used for treating pulmonary arterial hypertension..
STORAGE: Tablets should be kept at room temperature, 15-
30°C
(59-86°F).
PRESCRIBED FOR: Sildenafil is
used for the treatment of erectile dysfunction of either organic
(medical
condition) or psychogenic (psychological) cause and for pulmonary
arterial hypertension.
DOSING: Sildenafil is rapidly absorbed. Maximum
observed plasma
concentrations are reached within 30 to 120 minutes (median 60
minutes) of
oral dosing in the fasted state. When sildenafil is taken with
a high fat
meal, the rate of absorption is reduced, with an average delay
in the time
to maximal concentration of 1 hour.
DRUG INTERACTIONS: Sildenafil increases the
effects
of the blood pressure lowering medications. It also increases the blood pressure lowering effects of nitrates, e.g. isosorbide
dinitrate
(Isordil), isosorbide mononitrate (Imdur, Ismo, Monoket),
nitroglycerin
(Nitro-Dur, Transderm-Nitro) that are used primarily for treating angina. Patients taking nitrates should
not receive
sildenafil.
Cimetidine (Tagamet), erythromycin, ketoconazole (Nizoral),
itraconazole
(Sporanox) and mibefradil (Posicor) can cause marked increases
in the
amount of sildenafil in the body. Patients taking these
medications should
be observed carefully if sildenafil is used.
It is expected that rifampin will decrease blood levels of
sildenafil
and probably reduce its effectiveness.
PREGNANCY: Although extensive testing in animals has
demonstrated no negative effects on the fetus, sildenafil has
not been
studied in pregnant women. There is no effect on sperm count or
motility
of sperm in men.
NURSING MOTHERS: It is not
known whether sildenafil is excreted into breast milk.
SIDE EFFECTS: Approximately 15% of persons taking
sildenafil
experience side effects. The most common side effects are
facial flushing
(1 in 10), headaches (1 in 6), stomach pain, nasal congestion,
nausea,
diarrhea, and an
inability to differentiate between the colors green and blue. Rare cases
of sudden loss of hearing have been reported with phosphodiesterase inhibitors
such as sildenafil, sometimes with ringing in the ears and dizziness. If
changes in hearing occur, patients should discontinue their sildenafil and seek
immediate medical
attention.
Reference: FDA Prescribing Information
Last Editorial Review: 10/19/2007
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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