What is sildenafil?
Sildenafil (brand name: Viagra) is a medicine that doctors prescribe
to help men who have erectile dysfunction have sex. Erectile dysfunction
is the inability of the penis to become rigid (hard), or to stay rigid
long enough to finish having sex. Sildenafil helps maintain an erection.
How should I take sildenafil?
Follow your doctor's instructions. Usually, a man takes 1 tablet 30
minutes to 1 hour before he plans to have sex. You should not take more
than 1 tablet in 24 hours. The medicine comes in tablets of 25 mg, 50
mg and 100 mg. Most patients start with 50 mg.
Even if you take sildenafil, you still need physical and mental stimulation
and desire to have an erection. If your first dose of Viagra doesn't
help, call your doctor. Your doctor may want to change your tablet strength.
Dosage
For most patients, the recommended dose is 50 mg taken, as needed,
approximately 1 hour before sexual activity. However, VIAGRA may be
taken anywhere from 4 hours to 0.5 hour before sexual activity. Based
on effectiveness and toleration, the dose may be increased to a maximum
recommended dose of 100 mg or decreased to 25 mg. The maximum recommended
dosing frequency is once per day.
The following factors are associated with increased plasma levels
of sildenafil: age > 65 (40% increase in AUC), hepatic impairment
(e.g., cirrhosis, 80%), severe renal impairment (creatinine clearance
< 30 mL/min, 100%), and concomitant use of potent cytochrome P450
3A4 inhibitors [ketoconazole, itraconazole, erythromycin (182%), saquinavir
(210%)]. Since higher plasma levels may increase both the efficacy and
incidence of adverse events, a starting dose of 25 mg should be considered
in these patients.Ritonavir greatly increased the systemic level of
sildenafil in a study of healthy, non-HIV infected volunteers (11-fold
increase in AUC, see DRUG INTERACTIONS.) Based on these pharmacokinetic
data, it is recommended not to exceed a maximum single dose of 25 mg
of VIAGRA in a 48 hour period.
VIAGRA was shown to potentiate the hypotensive effects of nitrates and
its administration in patients who use nitric oxide donors or nitrates
in any form is therefore contraindicated.When VIAGRA is co-administered
with an alpha-blocker, patients should be stable on alpha- blocker therapy
prior to initiating VIAGRA treatment and VIAGRA should be initiated
at the lowest dose
Before purchasing Viagra (sildenafil citrate) online, you need to
make sure that Viagra's right for you. Visit Pfizer's official Viagra
site and read for detailed information on the drug, including possibly
dangerous drug interactions. If you are taking any medications or have
any health problems, you should consult with your family doctor or pharmacist
before buying Viagra online.An erection is produced via a complex chain
of events, involving signals from the nervous system and the release
of chemical messengers within the tissues of the penis. One of these
chemical messengers is called cyclic GMP.Cyclic GMP causes the blood
vessels in the penis to widen by relaxing a thin layer of muscle found
in the blood vessel walls. This allows more blood to enter the penis,
which ultimately results in the penis becoming rigid and erect.Cyclic
GMP is normally broken down by another chemical in the body called phosphodiesterase
type 5. Sildenafil works by preventing the action of phosphodiesterase
type 5, thus stopping the breakdown of cyclic GMP. This means that the
blood vessels are kept dilated for longer, improving blood flow to the
penis and maintaining an erection.
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