Sildenafil
Systematic (IUPAC) name
1-[4-ethoxy-3-(6,7-dihydro-1-methyl- 7-oxo-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-5-yl) phenylsulfonyl]-4-methylpiperazine citrate
Identifiers
CAS number	139755-83-2
ATC code	G04BE03
PubChem	5281023
DrugBank	APRD00556
Chemical data
Formula	C22H30N6O4S
Mol. mass	base: 474. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general A citrate can refer either to the Conjugate base of Citric acid, (C3H5O(COO33&minus or to the Esters of citric CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to The Anatomical Therapeutic Chemical Classification System is used for the classification of drugs It is controlled by the WHO Collaborating Centre for Drug A section of the Anatomical Therapeutic Chemical Classification System. PubChem is a Database of chemical Molecules The system is maintained by the National Center for Biotechnology Information (NCBI a component The DrugBank database available at the University of Alberta is a unique Bioinformatics and Cheminformatics resource that combines detailed drug (i A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 The molecular mass (abbreviated m of a substance, more commonly referred to as molecular weight and abbreviated as MW, is the Mass of one 6 g/mol
SMILES	eMolecules & PubChem
Pharmacokinetic data
Bioavailability	40%
Metabolism	Hepatic
Half life	3-4h
Excretion	CYP3A4
Therapeutic considerations
Pregnancy cat.	N/A
Legal status	℞ Prescription only
Routes	Oral

Sildenafil citrate, sold under the names Viagra, Revatio and under various other names, is a drug used to treat male erectile dysfunction (impotence) and pulmonary arterial hypertension (PAH), developed by the pharmaceutical company Pfizer. Nu Virgos (also known as ВИА Гра - an allusion both to VIA Gra due to the first three letters which stand for vocal-instrumental band and Viagra) is a Medication, also referred to as medicine, can be loosely defined as any substance intended for use in the diagnosis cure mitigation treatment or prevention of disease In Medicine, pulmonary hypertension (PH is an increase in blood pressure in the Pulmonary artery, Pulmonary vein, or pulmonary capillaries together known Pfizer Incorporated ( is a major Pharmaceutical company, which ranks number one in the world in sales Its primary competitors on the market are tadalafil (Cialis), and vardenafil (Levitra). Tadalafil is an orally administered drug for treating impotence ( Erectile dysfunction) that initially was developed by the Biotechnology company ICOS Vardenafil ( INN) is a PDE5 inhibitor used for treating impotence ( Erectile dysfunction) that is sold under the trade name Levitra ( Bayer

Contents 1 History 2 Mechanism of action 3 Dosage and price 3.1 Market structure 4 Contraindications 5 Side effects 6 Other uses 6.1 Pulmonary hypertension 6.2 Raynaud's phenomenon 6.3 Altitude sickness 6.4 Duchenne/Becker Muscular Dystrophy 7 Non-medical use 7.1 Aphrodisiac 7.2 Recreational use 7.3 Prevention of plant wilting 7.4 Jet lag research 8 Chemical synthesis 9 See also 10 References 11 External links

History

Sildenafil (compound UK-92,480) was synthesized by a group of pharmaceutical chemists working at Pfizer's Sandwich, Kent research facility in England. Sandwich is a historic town in Kent, south-east England. It was one of the Cinque Ports and still has many original medieval buildings It was initially studied for use in hypertension (high blood pressure) and angina pectoris (a symptom of ischaemic cardiovascular disease). Hypertension, also referred to as high blood pressure, HTN or HPN, is a medical condition in which the Blood pressure is chronically elevated Angina pectoris, commonly known as angina, is severe Chest pain due to Ischemia (a lack of blood and hence Oxygen supply of the heart In Medicine, ischemia ( Greek ισχαιμία, isch- is restriction hema or haema is Blood) is a restriction Cardiovascular disease or cardiovascular diseases refers to the class of diseases that involve the Heart or Blood vessels ( arteries and The first clinical trials were conducted in Morriston Hospital in Swansea. Morriston Hospital is a 750 bed hospital located in Cwmrhydyceirw near Morriston, Wales, UK. Swansea ( Abertawe "mouth of the Tawe " is a city and county in Wales. [2] Phase I clinical trials under the direction of Ian Osterloh suggested that the drug had little effect on angina, but that it could induce marked penile erections. In health care clinical trials are conducted to allow safety and Efficacy data to be collected for new drugs or devices Ian Osterloh is a clinical researcher for Pfizer Inc who led the development of sildenafil citrate (Viagra as well as a number of Pfizer medications for Cardiovascular The erection of the Penis, Clitoris or a Nipple is its enlarged and firm state ^[1][2] Pfizer therefore decided to market it for erectile dysfunction, rather than for angina. The drug was patented in 1996, approved for use in erectile dysfunction by the Food and Drug Administration on March 27, 1998, becoming the first pill approved to treat erectile dysfunction in the United States, and offered for sale in the United States later that year. A patent is a set of Exclusive rights granted by a State to an inventor or his assignee for a fixed period of time in exchange for a disclosure of an Year 1996 ( MCMXCVI) was a Leap year starting on Monday (link will display full 1996 Gregorian calendar) Events 196 BC - Ptolemy V ascends to the throne of Egypt. 1309 - Pope Clement V excommunicates Year 1998 ( MCMXCVIII) was a Common year starting on Thursday (link will display full 1998 Gregorian calendar) ^[3] It soon became a great success: annual sales of Viagra in the period 1999–2001 exceeded $1 billion. Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar.

The British press portrayed Peter Dunn and Albert Wood as the inventors of the drug, a claim which Pfizer disputes. ^[4] Their names are on the manufacturing patent application drug, but Pfizer claims this is only for convenience.

Even though sildenafil is available only by prescription from a doctor, it was advertised directly to consumers on U. S. TV (famously being endorsed by former United States Senator Bob Dole and football star Pelé). The United States Senate is the Upper house of the bicameral United States Congress, the Lower house being the House of Representatives Robert Joseph "Bob" Dole (born July 22 1923 is an attorney and retired United States Senator from Kansas from 1969–1996 serving part of that time Association football, more commonly known as football or soccer, is a Team sport played between two teams of eleven players and is widely considered Numerous sites on the Internet offer Viagra for sale after an "online consultation," often a simple web questionnaire. The "Viagra" name has become so well known that many fake aphrodisiacs now call themselves "herbal Viagra" or are presented as blue tablets imitating the shape and colour of Pfizer's product. Viagra is also informally known as "Vitamin V", "the Blue Pill", as well as various other nicknames.

In February 2007, it was announced that Boots the Chemist would trial over the counter sales of Viagra in stores in Manchester, England. This article is about a former British company which has now merged to form Alliance Boots, as a result information on this page may be out of date Over-the-counter (OTC drugs are medicines that may be sold without a prescription, in contrast to Prescription drugs The name "over-the-counter" England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Men aged between 30 and 65 would be eligible to buy four tablets after a consultation with a pharmacist. Pharmacists are Health professionals who practice the art and science of Pharmacy. ^[5]

Pfizer's worldwide patents on sildenafil citrate will expire in 2011–2013. The UK patent held by Pfizer on the use of PDE5 inhibitors (see below) as treatment of impotence was invalidated in 2000 because of obviousness; this decision was upheld on appeal in 2002. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located A phosphodiesterase type 5 inhibitor, often shortened to PDE5 inhibitor, is a drug used to block the degradative action of Phosphodiesterase type 5 on

Mechanism of action

Part of the physiological process of erection involves the parasympathetic nervous system causing the release of nitric oxide (NO) in the corpus cavernosum of the penis. The parasympathetic Nervous system ( PSNS) is a division of the Autonomic nervous system (ANS along with the Sympathetic nervous system Nitric oxide or nitrogen monoxide is a Chemical compound with Chemical formula N[[Oxygen O]] The corpus cavernosum penis is one of a pair of sponge-like regions of Erectile tissue which contain most of the Blood in the male Penis during Erection NO binds to the receptors of the enzyme guanylate cyclase 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. Guanylate cyclase ( also known as guanylyl cyclase or GC) is a Lyase Enzyme. Cyclic guanosine monophosphate ( cGMP) is a Cyclic nucleotide derived from Guanosine triphosphate (GTP Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder On entering the cavernous structure from the Deep_artery_of_the_penis the arteries divide into branches which are supported and enclosed by the Trabeculae.

Sildenafil is a potent and selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum. cGMP-specific phosphodiesterase type 5 is an Enzyme ( from the Phosphodiesterase class The corpus cavernosum penis is one of a pair of sponge-like regions of Erectile tissue which contain most of the Blood in the male Penis during Erection The molecular structure of sildenafil 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. Without sexual stimulation, and therefore lack of activation of the NO/cGMP system, sildenafil should not cause an erection. Other drugs that operate by the same mechanism include tadalafil (Cialis) and vardenafil (Levitra). Tadalafil is an orally administered drug for treating impotence ( Erectile dysfunction) that initially was developed by the Biotechnology company ICOS Vardenafil ( INN) is a PDE5 inhibitor used for treating impotence ( Erectile dysfunction) that is sold under the trade name Levitra ( Bayer

Sildenafil is metabolised by hepatic enzymes and excreted by both the liver and kidneys. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins The liver is a vital organ in the human body and is present in Vertebrates and some other animals The kidneys are complicated organs that have numerous biological roles If taken with a high-fat meal, there may be a delay in absorption of sildenafil and the peak effect might be reduced slightly as the plasma concentration will be lowered.

Dosage and price

As with all prescription drugs, proper dosage is at the discretion of a licensed medical doctor. A prescription drug is a licensed medicine that is regulated by legislation to require a prescription before it can be obtained A physician, medical practitioner or medical doctor who practices Medicine, and is concerned with maintaining or restoring human Health The dose of sildenafil for erectile dysfunction is 25 mg to 100 mg taken not more than once per day between 30 minutes and 4 hours prior to sexual intercourse. Sexual intercourse, in its biological sense is the act in which the male reproductive organ (in humans and other higher animals enters the female reproductive tract

It is usually recommended to start with a dosage of 50 mg and then lower or raise the dosage as appropriate. The drug is sold in three dosages (25, 50, and 100 mg), all three costing about US$10 per pill. Name-brand Viagra sildenafil is not scored and a fairly hard coating makes it more difficult to accurately cut the pills in half, even with a pill cutter.

The dosage for pulmonary arterial hypertension (Revatio) is one 20 mg tablet three times a day.

Viagra pills are blue and diamond-shaped with the words "Pfizer" engraved on one side, and "VGR xx" (where xx stands for "25", "50" or "100", the dose of that pill in milligrams) engraved on the other. Words are not printed on the pills.

Revatio pills, which are used for PAH, are white, round, film-coated tablets imprinted with "RVT 20" on one side and "Pfizer" on the other.

Market structure

In 2000, Viagra sales accounted for 92 per cent of the global market for prescribed Erectile Dysfunction pills. (pdf) By 2007, Viagra's global share had plunged to about 50 percent due to entry of Cialis and Levitra, along with several other counterfeits and clones. Tadalafil is an orally administered drug for treating impotence ( Erectile dysfunction) that initially was developed by the Biotechnology company ICOS Vardenafil ( INN) is a PDE5 inhibitor used for treating impotence ( Erectile dysfunction) that is sold under the trade name Levitra ( Bayer

Contraindications

Contraindications include:

• When taking nitric oxide donors, organic nitrites and nitrates, such as glyceryl trinitrate (nitroglycerin), sodium nitroprusside, amyl nitrite ("poppers")^[6]
• 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)

Side effects

Amongst sildenafil's rare but serious adverse effects are: priapism, severe hypotension, myocardial infarction, ventricular arrhythmias, stroke and increased intraocular pressure. In Medicine, a contraindication (pronounced as contra-indication is a condition or factor that increases the Risks involved in using a particular drug, Sodium nitroprusside is the Chemical compound with the formula Na2·2H2O Amyl nitrite is the Chemical compound with the formula C5H11ONO Poppers is the Street term for various Alkyl nitrites taken for recreational purposes through direct inhalation, particularly Amyl nitrite Sexual intercourse, in its biological sense is the act in which the male reproductive organ (in humans and other higher animals enters the female reproductive tract This is an article about the rock music band "Circulatory System" Chronic liver disease is a liver disease of slow process and persisting over a long period of time resulting in a progressive destruction of the Liver. Renal function, in Nephrology, is an indication of the state of the Kidney and its role in Renal physiology. In Physiology and Medicine, hypotension refers to an abnormally low Blood pressure. A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply The vertebrate retina is a light sensitive part inside the inner layer of the Eye. A phosphodiesterase is any Enzyme that breaks a Phosphodiester bond. Priapism (πριαπισμός is a potentially harmful and painful medical condition in which the erect Penis does not return to its flaccid state despite In Physiology and Medicine, hypotension refers to an abnormally low Blood pressure. Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply Ventricular tachycardia ( V-tach or VT) is a Tachycardia, or fast heart rhythm that originates in one of the ventricles of the Heart A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain Intraocular pressure (IOP is the fluid Pressure inside the Eye.

Common side effects include sneezing, headache, flushing, dyspepsia, palpitations and photophobia. A sneeze (or sternutation) is a semi-autonomous Convulsive expulsion of Air from the Lungs, most commonly caused by foreign particles A headache ( cephalalgia in medical terminology is a condition of pain in the Head; sometimes Neck or upper back pain may also be interpreted For a person to flush is to become markedly Red in the Face and often other areas of the skin from various physiological conditions Dyspepsia (from the Greek "δυς-" (Dys- and "πέψη" (Pepse known in plain English as indigestion, meaning hard A palpitation (medical term ectopic heart beat) is an abnormal awareness of the beating of the Heart, whether it is too slow too fast irregular Photophobia is a Symptom of excessive sensitivity to Light and the aversion to Sunlight or well-lit places

Care should be exercised by patients who are also taking Protease inhibitors for the treatment of HIV. For natural protease inhibitors please see Protease inhibitor (biology Protease inhibitors (PIs are a class of Medications used Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome Protease inhibitors inhibit the metabolism of sildenafil, effectively multiplying the plasma levels of sildenafil, increasing the incidence and severity of side-effects. It is recommended that patients using protease inhibitors limit their use of sildenafil to no more than one 25-mg dose every 48 hours.

Some sildenafil users have complained of seeing everything tinted blue (cyanopsia). Cyanopsia is a medical term for seeing everything tinted with Blue. ^[7]. Some complained of blurriness and loss of peripheral vision. Peripheral vision is a part of vision that occurs outside the very center of gaze In May of 2005, the U.S. Food and Drug Administration found that sildenafil could lead to vision impairment^[8] and a number of studies have linked sildenafil use with nonarteritic anterior ischemic optic neuropathy. The United States of America —commonly referred to as the ^{[9][10][11][12][13][14]}

In October 2007, the FDA announced that the labeling for all PDE5 inhibitors, including sildenafil, requires a more prominent warning of the potential risk of sudden hearing loss as the result of postmarketing reports of deafness associated with use of PDE5 inhibitors. ^[15]

When used with an alpha blocker, hypotension (low blood pressure) may occur, but this effect does not occur if they are taken at least four hours apart. Alpha blockers (or adrenergic alpha-antagonists) are agents that act as antagonists of alpha adrenergic receptors Classification They can be divided In Physiology and Medicine, hypotension refers to an abnormally low Blood pressure. ^[16]

Other uses

Pulmonary hypertension

As well as erectile dysfunction, sildenafil citrate is also effective in the rare disease pulmonary arterial hypertension (PAH). A rare disease (sometimes known as an orphan disease has such a low Prevalence in a population that a doctor in a busy General practice would not In Medicine, pulmonary hypertension (PH is an increase in blood pressure in the Pulmonary artery, Pulmonary vein, or pulmonary capillaries together known It relaxes the arterial wall, leading to decreased pulmonary arterial resistance and pressure. This in turn reduces the workload of the right ventricle of the heart and improves symptoms of right-sided heart failure. In the Heart, a ventricle is a heart chamber which collects Blood from an atrium (another heart chamber that is smaller than a ventricle and Heart failure is a Cardiac condition that occurs when a problem with the structure or function of the Heart impairs its ability to supply Because PDE-5 is primarily distributed within the arterial wall smooth muscle of the lungs and penis, sildenafil acts selectively in both these areas without inducing vasodilation in other areas of the body. Pfizer submitted an additional registration for sildenafil to the FDA, and sildenafil was approved for this indication in June 2005. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. The preparation is named Revatio, to avoid confusion with Viagra, and the 20 milligram tablets are white and round. Sildenafil joins bosentan and prostacyclin-based therapies for this condition. Bosentan (BOZENTAN is a dual Endothelin receptor antagonist important in the treatment of Pulmonary artery hypertension (PAH Prostacyclin (or PGI2) is a member of the family of Lipid Molecules known as Eicosanoids. ^[17]

Raynaud's phenomenon

In 2005, Dr. Roland Fries and colleagues reported that sildenafil cut the frequency of Raynaud's phenomenon attacks, reduced their duration by roughly one half, and more than quadrupled the mean capillary blood velocity. Raynaud's phenomenon (reɪˈnoʊz (rāy-NŌZ in Medicine, is a vasospastic disorder causing discoloration of the Fingers Toes and occasionally This was a double-blind, placebo-controlled crossover trial and the patients had both the primary and secondary forms and had all discontinued the more conventional treatments for this. ^[18]

Altitude sickness

Sildenafil 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. High altitude pulmonary edema (HAPE is a life-threatening form of non-cardiogenic Pulmonary edema that occurs in otherwise healthy Mountaineers at altitudes above ^[19][20] While this effect has only recently been discovered, sildenafil is already becoming an accepted treatment for this condition, particularly in situations where the standard treatment of rapid descent has been delayed for some reason. ^[21]

Duchenne/Becker Muscular Dystrophy

Sildenafil has recently been used to enhance cGMP signaling, specifically downstream and independent of NO formation, in dystrophin-deficient mouse hearts. Dystrophin is a rod-shaped Cytoplasmic Protein, and a vital part of a Protein complex that connects the Cytoskeleton of a Muscle fiber Chronic treatment improved contractile performance, myocardial metabolic status, and sarcolemmal integrity, highlighting its potential clinical avenue for the treatment of the dystrophin-related cardiomyopathies. ^[22]

Non-medical use

Aphrodisiac

Sildenafil is commonly and increasingly used as an aphrodisiac, i. e. to increase sexual desire. Libido in its common usage means Sexual desire however more technical definitions such as those found in the work of Carl Jung, are more general referring to libido However, there is no clinical evidence that it has aphrodisiac activity, because it does not have any direct effect on the brain, although increased ability to attain an erection may be interpreted as increased sexual arousal by users of these drugs.

Recreational use

Viagra's popularity with young adults has increased over the years. ^[23] It is sometimes used recreationally. Some users mix Viagra with methylenedioxymethamphetamine (MDMA, ecstasy) in an attempt to compensate for the side effect common to many amphetamines of erectile dysfunction, a combination known as "sextasy", "rockin' and rollin'", or 'trail mix'. MDMA ( 34-methylenedioxy- N -methylamphetamine) most commonly known today by the street name Ecstasy (often abbreviated E, X, Poly drug use refers to the use two or more Psychoactive drugs in combination to achieve a particular effect "

Prevention of plant wilting

A low-concentration solution of sildenafil 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 leads to the production of cGMP whose degradation by PDE5 is inhibited by sildenafil. ^[24]

Jet lag research

The 2007 Ig Nobel Prize in Aviation went to Patricia V. The Ig Nobel Prizes are a Parody of the Nobel Prizes and are given each year in early October — around the time the recipients of the genuine Nobel Prizes are Agostino, Santiago A. Plano and Diego A. Golombek of Universidad Nacional de Quilmes, Argentina, for their discovery that Viagra aids jet lag recovery in hamsters. Jet lag, also jetlag or jet-lag, is a physiological condition which is a consequence of alterations to Circadian rhythms it is classified ^[25] Their research was published in the Proceedings of the National Academy of Sciences. The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United ^[26]

Chemical synthesis

The preparation steps for synthesis of Viagra (sildenafil citrate) are as follows:

1. Methylation of 3-propylpyrazole-5-carboxylic acid ethyl ester with hot dimethyl sulfate. Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates.
2. Hydrolysis with aqueous NaOH to free acid. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions
3. Nitration with oleum/fuming nitric acid. Nitration is a general Chemical process for the introduction of a nitro group into a Chemical compound.
4. Carboxamide formation with refluxing thionyl chloride/NH4OH.
5. Reduction of nitro group to amino. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state
6. Acylation with 2-ethoxybenzoyl chloride. In Chemistry, acylation (rarely but more formally alkanoylation) is the process of adding an Acyl group to a compound
7. Cyclization.
8. Sulfonation to the chlorosulfonyl derivative. Sulfonic acid is an unstable Acid with the formula H-S(=O2-OH
9. Condensation with 1-methylpiperazine. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase ^[27]

See also

• Tadalafil (Cialis)
• Vardenafil (Levitra)
• Yohimbine

References

External links

• Home page for Viagra
• Home page for Revatio
• Pfizer Pharmaceutical (Company website) - manufacturer of Viagra; prescribing information for Viagra and prescribing information for Revatio available in PDF format.
• FDA Web Site for Viagra Consumer Information
• FDA current Viagra label (a form of clinical information and report)
• MedlinePLUS drug Information - Side Effects of sildenafil
• How Viagra Works - Howstuffworks article
• Does Viagra Keep Flowers From Wilting?

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