Sildenafil Citrate (UK Viagra) Information
Sildenafil citrate, sold as
"Viagra" UK, "Revatio" and under various other trade names,
is a drug (Viagra UK) used to treat erectile dysfunction
and pulmonary arterial hypertension (PAH). Sildenafil
citrate (Viagra UK) was developed by and is being marketed
by the pharmaceutical company Pfizer. Sildenafil citrate
(Viagra UK) acts by inhibiting cGMP specific
phosphodiesterase type 5, an enzyme that regulates blood
flow in the penis. Since becoming available in 1998,
sildenafil citrate (Viagra UK) has been the prime treatment
for erectile dysfunction; sildenafil citrate's (Viagra UK)
primary competitors on the market are tadalafil (Cialis UK)
and vardenafil (Levitra UK).
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preseciption for GENUINE UK VIAGRA – please
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Mechanism of
action of Genuine Viagra UK
The
mechanism of action of sildenafil citrate (viagra UK)
involves the release of nitric oxide (NO) in the corpus
cavernosum of the penis. NO binds to the receptors of the
enzyme guanylate cyclase in the sildenafil citrate (viagra
UK), which results in increased levels of cyclic guanosine
monophosphate (cGMP), leading to smooth muscle relaxation
(vasodilation) of the intimal cushions of the helicine
arteries, resulting in increased inflow of blood and an
erection.[14] Robert F. Furchgott won the
Nobel Prize in Physiology or Medicine in 1998 for his
discovery and analysis of endothelium-derived relaxing
factor, a key part of the NO mechanism of action.
Sildenafil citrate (viagra UK) is a potent and selective
inhibitor of cGMP specific phosphodiesterase type 5 (PDE5),
which is responsible for degradation of cGMP in the corpus
cavernosum. The molecular structure of sildenafil citrate
(viagra UK) is similar to that of cGMP and acts as a
competitive binding agent of PDE5 in the corpus cavernosum,
resulting in more cGMP and better
erections.[14] Without sexual stimulation, and
therefore lack of activation of the NO/cGMP system,
sildenafil citrate (viagra UK) should not cause an
erection. Other drugs that operate by the same mechanism
include tadalafil (Cialis UK) and vardenafil (Levitra UK).
Sildenafil citrate (viagra UK) is metabolised by liver
enzymes and excreted by both the liver and kidneys. If
sildenafil citrate (viagra UK) is taken with a high-fat
meal, absorption is reduced; the time taken to reach the
maximum plasma concentration of sildenafil citrate (viagra
UK) increases by around one hour, and the maximum
concentration itself of sildenafil citrate (viagra UK) is
decreased by nearly one-third.[15]
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Uses of
Genuine Viagra UK
Sexual
dysfunction uses of Viagra UK
The
primary indication of sildenafil citrate (viagra UK) is
treatment of erectile dysfunction (inability to sustain a
satisfactory erection to complete intercourse, also known
as "male impotence"). Sildenafil citrate's (viagra UK) use
is now standard treatment for erectile dysfunction in all
settings, including diabetes.[16]
People on antidepressants may experience sexual
dysfunction, either as a result of their illness or as a
result of their treatment. A 2003 study showed that
sildenafil citrate (viagra UK) improved sexual function in
men in this situation.[17] Following up to earlier reports
from 1999,[18]
the same
researchers found that sildenafil citrate (viagra UK) was
able to improve sexual function in female patients on
antidepressants as well.[19]
Pulmonary
hypertension uses of Viagra UK
As
well as erectile dysfunction, sildenafil citrate (viagra
UK) is also effective in the rare disease pulmonary
arterial hypertension (PAH). Sildenafil citrate (viagra UK)
relaxes the arterial wall, leading to decreased pulmonary
arterial resistance and pressure. This effect of sildenafil
citrate (viagra UK), in turn, reduces the workload of the
right ventricle of the heart and improves symptoms of
right-sided heart failure. Because PDE-5 is primarily
distributed within the arterial wall smooth muscle of the
lungs and penis, sildenafil citrate (viagra UK) acts
selectively in both these areas without inducing
vasodilation in other areas of the body. Pfizer submitted
an additional registration for sildenafil citrate (viagra
UK) to the FDA, and sildenafil citrate (viagra UK) was
approved for this indication in June 2005. The preparation
is named Revatio, to avoid confusion with Viagra UK, and
the 20 milligram tablets are white and round. Sildenafil
citrate (viagra UK) joins bosentan and prostacyclin-based
therapies for this condition.[20]
Altitude
sickness uses of Viagra UK
Sildenafil citrate (viagra UK)
has been shown to be useful for the prevention and
treatment of High-altitude pulmonary edema associated with
altitude sickness such as that suffered by mountain
climbers.[21][22] While this effect has only
recently been discovered, sildenafil citrate (viagra UK) is
already becoming an accepted treatment for this condition,
in particular in situations where the standard treatment of
rapid descent has been delayed for some
reason.[23]
Use in sports
of Viagra UK
Professional sports players
have been using drugs such as Viagra UK, thinking that the
opening of their blood vessels will enrich their muscles,
therefore enhancing their performance.[24]
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Non-medical
use of Viagra UK
Recreational
use of Viagra UK
Sildenafil citrate's (viagra
UK) popularity with young adults has increased over the
years.[25]
Sildenafil
citrate's (viagra UK) trade name "Viagra" UK is widely
recognized in popular culture, and the sildenafil citrate's
(viagra UK) association with treating erectile dysfunction
has led to the recreational use of sildenafil citrate
(viagra UK).[26] The reasons behind such use of
sildenafil citrate (viagra UK) include the belief that
sildenafil citrate (viagra UK) increases libido, that
sildenafil citrate (viagra UK) improves sexual
performance,[26] or that sildenafil citrate
(viagra UK) permanently increases penis size. Studies on
the effects of viagra UK when used recreationally are
limited, but suggest that sildenafil citrate (viagra UK)
has little effect when used by those not suffering from
erectile dysfunction, and having sex within a stable
relationship. In one study, a 25mg dose of sildenafil
citrate (viagra UK) was shown to cause no significant
change in erectile quality, but the sildenafil citrate
(viagra UK)did reduce the post-ejaculatory refractory
time.[27] This study also noted a
significant placebo effect in the control group for Viagra
UK.[27]
Unprescribed recreational use of sildenafil citrate (viagra
UK) and other PDE-5 Inhibitors is noted as particularly
high among users of illegal drugs.[28][29] Sildenafil citrate (viagra UK)
is sometimes used to counteract the effects of other
substances, often illicit.[26] Some users mix sildenafil
citrate (viagra UK) with methylenedioxymethamphetamine
(MDMA, ecstasy), other stimulants, or opiates in an attempt
to compensate for the common side-effect of erectile
dysfunction, a combination known as "sextasy," "rockin' and
rollin'," or "trail mix."[26] Mixing sildenafil citrate
(viagra UK) with amyl nitrite is particularly dangerous,
and is potentially fatal.[26]
Prevention of
plant wilting use of Viagra UK
A
low-concentration solution of sildenafil citrate (viagra
UK) in water significantly prolongs the time before cut
flowers wilt; one experiment showed a doubling in time from
one week to two weeks. The mechanism of action is similar
to that in humans: nitric oxide in the sildenafil citrate
(viagra UK) leads to the production of cGMP whose
degradation by PDE5 is inhibited by sildenafil citrate
(viagra UK).[30]
Jet lag
research relating to Viagra UK
The
2007 Ig Nobel Prize in Aviation went to Patricia V.
Agostino, Santiago A. Plano and Diego A. Golombek of
Universidad Nacional de Quilmes, Argentina, for their
discovery that Viagra UK aids jet lag recovery in
hamsters.[31] Their research about sildenafil
citrate (viagra UK) was published in the Proceedings of the
National Academy of Sciences.[32]
Analogues of
Sildenafil Citrate (Viagra UK)
Acetildenafil is a structural
analogue of sildenafil citrate (viagra UK), one of the PDE5
inhibitors found in a number of "herbal" aphrodisiac
products sold over-the-counter (sometimes called "generic
Viagra"). This class of analogues have not undergone any of
the rigorous testing that drugs like sildenafil citrate
(viagra UK) have passed, and thus have an unknown
side-effect profile.[33] Some attempts have been made to
ban these drugs, but progress has been slow so far, as,
even in those jurisdictions that have laws targeting
designer drugs, the laws are drafted to ban analogues of
illegal drugs of abuse, rather than analogues of
prescription medicines. However, at least one court case
has resulted in a product (an analogue sildenafil citrate
[viagra UK]) being taken off the market.[34]
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Dosage of
Viagra UK
Viagra
UK pills are blue and diamond-shaped with the words
"Pfizer" engraved on one side, and "VGR xx" (where xx
stands for "50" or "100", the dose of that Viagra UK pill
in milligrams) engraved on the other. The dose of
sildenafil citrate (viagra UK) for erectile dysfunction is
50 mg to 100 mg taken not more than once per day
between 30 minutes and 4 hours prior to sexual intercourse.
The dosage for pulmonary arterial hypertension (Revatio) is
one 20 mg tablet three times a day. Revatio pills are
white, round, film-coated tablets imprinted with "RVT 20"
embossed on one side (Viagra UK).[35]
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Contraindications
of Viagra UK
Contraindications of sildenafil
citrate (viagra UK) include:
•
When taking nitric oxide donors, organic nitrites and
nitrates, such as glyceryl trinitrate (nitroglycerin),
sodium nitroprusside, amyl nitrite
("poppers")[36]
• In men for whom sexual intercourse is inadvisable due to
cardiovascular risk factors
• Severe hepatic impairment (decreased liver function)
• Severe impairment in renal function
• Hypotension (low blood pressure)
• Recent stroke or heart attack
• Hereditary degenerative retinal disorders (including
genetic disorders of retinal phosphodiesterases)
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Side-effects
of Viagra UK
In
clinical trials, the most common adverse effects of
sildenafil citrate (viagra UK) use included headache,
flushing, dyspepsia, nasal congestion and impaired vision,
including photophobia and blurred
vision.[37]
Some sildenafil
citrate (viagra UK) users have complained of seeing
everything tinted blue (cyanopsia).[38] Some sildenafil citrate (viagra
UK) users complained of blurriness and loss of peripheral
vision. In July 2005, the U.S. Food and Drug Administration
found that sildenafil citrate (viagra UK) could lead to
vision impairment in rare cases[39] and a number of studies have
linked sildenafil citrate (viagra UK) use with nonarteritic
anterior ischemic optic neuropathy.[40][41][42][43][44][45]
Rare but serious adverse effects found through
postmarketing surveillance of sildenafil citrate (viagra
UK) include priapism, severe hypotension, myocardial
infarction (heart attack), ventricular arrhythmias, stroke,
increased intraocular pressure, and sudden hearing
loss.[37] As a result of these
postmarketing reports about sildenafil citrate (viagra UK),
in October 2007, the FDA announced that the labeling for
all PDE5 inhibitors, including sildenafil citrate (viagra
UK), required a more prominent warning of the potential
risk of sudden hearing loss.[46]
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Interactions
with Viagra UK
Care
should be exercised by patients using sildenafil citrate
(viagra UK) that are also taking protease inhibitors for
the treatment of HIV. Protease inhibitors inhibit the
metabolism of sildenafil citrate (viagra UK), effectively
multiplying the plasma levels of sildenafil citrate (viagra
UK), increasing the incidence and severity of side-effects
of sildenafil citrate (viagra UK). It is recommended that
patients using protease inhibitors limit their use of
sildenafil citrate (viagra UK) to no more than one
25 mg (of sildenafil citrate [viagra UK]) dose every
48 hours.
Concomitant use of sildenafil citrate (viagra UK) and an
alpha blocker may lead to low blood pressure, but this
effect does not occur if sildenafil citrate (viagra UK) and
the alpha blocker are taken at least four hours
apart.[47]
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Chemical
synthesis of Sildenafil Citrate (Viagra UK)
The
preparation steps for synthesis of sildenafil citrate
(viagra UK) are as follows:[48]
1. Methylation of
3-propylpyrazole-5-carboxylic acid ethyl ester with hot
dimethyl sulfate.
2. Hydrolysis with aqueous NaOH to free acid.
3. Nitration with oleum/fuming nitric acid.
4. Carboxamide formation with refluxing thionyl
chloride/NH4OH.
5. Reduction of nitro group to amino.
6. Acylation with 2-ethoxybenzoyl chloride.
7. Cyclization.
8. Sulfonation to the chlorosulfonyl derivative.
9. Condensation with 1-methylpiperazine.
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Notes about
Viagra UK
1.
Aubetawe Bro Morgannwg University NHS Trust (2008-07-04).
"Research at ABM". Viagra UK
2. "Sildenafil: an orally active type 5 cyclic GMP-specific
phosphodiesterase inhibitor for the treatment of penile
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PMID 8858389. Viagra UK
3. Terrett NK et al. (1996). "Sildenafil (Viagra), a potent
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4. Kling J (1998). "From hypertension to angina to Viagra"
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8. McGuire, Stephen (1 January 2007). "Cialis gaining
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10. Berenson, Alex (December 4, 2005). "Sales of Impotence
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11. Buy Genuine Prescription Viagra UK
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14. Webb, D.J.; Freestone, S.; Allen, M.J.; Muirhead, G.J.
(March 4, 1999). "Sildenafil citrate and
blood-pressure-lowering drugs: results of drug interaction
studies with an organic nitrate and a calcium antagonist".
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15. "Viagra Clinical Pharmacology". RxList.com. 2008.
Viagra UK
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UK
17. Nurnberg HG, Hensley PL, Gelenberg AJ, Fava M,
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18. Nurnberg HG, Hensley PL, Lauriello J, Parker LM, Keith
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18647982. Viagra UK
20. Pfizer, Inc. (June 6, 2005). "FDA Approves Pfizer's
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2005 News Releases. Pfizer. Viagra UK
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"Sildenafil inhibits altitude-induced hypoxemia and
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(3): 275–81. doi:10.1164/rccm.200406-804OC. PMID 15516532.
Viagra UK
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Viagra UK
23. Fagenholz PJ, Gutman JA, Murray AF, Harris NS (2007).
"Treatment of high altitude pulmonary edema at 4240 m in
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doi:10.1089/ham.2007.1055. PMID 17584008. Viagra UK
24. "Source: Roger Clemens, host of athletes pop Viagra to
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2008.
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drug arsenal". USAToday. Viagra UK
26. Smith, K; F Romanelli (2005). "Recreational use and
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Loro, G Lombardi and M Rizzo (2003). "Sildenafil does not
improve sexual function in men without erectile dysfunction
but does reduce the postorgasmic refractory time".
International Journal of Impotence Research 15: 225–228.
Viagra UK
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(2006). "The rise of Viagra among British illicit drug
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29. Eloi-Stiven, M; Channaveeraiah, N.a , Christos, P.J.c ,
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up straight". Student BMJ (9). Viagra UK
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4 October 2007. Viagra UK
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(2007). "Sildenafil accelerates reentrainment of circadian
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Sci. U.S.A. 104 (23): 9834–9. doi:10.1073/pnas.0703388104.
PMID 17519328. Viagra UK
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analogues in herbal products for erectile dysfunction.
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42. Pomeranz, H; Pomeranz HD, Smith KH, Hart WM, Egan RA
(2002). "Sildenafil-associated nonarteritic anterior
ischemic optic neuropathy". Ophthalmology 109 (3): 584–7.
doi:10.1016/S0161-6420(01)00976-9. PMID 11874765. Viagra UK
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44. "A case of nonarteritic ischemic optic neuropathy
(NAION) in a male patient taking sildenafil". Int J Clin
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UK
45. Akash, Raj; Akash R, Hrishikesh D, Amith P, Sabah S
(2005). "Case report: association of combined nonarteritic
anterior ischemic optic neuropathy (NAION) and obstruction
of cilioretinal artery with overdose of Viagra". J Ocul
Pharmacol Ther 24 (4): 315–7. doi:10.1089/jop.2005.21.315.
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46. "FDA Announces Revisions to Labels for Cialis, Levitra
and Viagra". United States Food and Drug Administration. 18
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47. Kloner RA (2005). "Pharmacology and drug interaction
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48. Dunn PJ (2005). "Synthesis of Commercial
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