VIAGRA ฎ (sildenafil citrate)

Viagra : the first oral treatment for male impotence and erectile dysfunction

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Sildenafil citrate, sold as Viagra, Revatio and under various other trade names, is a drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH).

It was developed and is being marketed by the pharmaceutical company Pfizer.

It acts by inhibiting cGMP specific phosphodiesterase type 5, an enzyme that regulates blood flow in the penis. Patient leaflet.

Since becoming available in 1998, sildenafil has been the prime treatment for erectile dysfunction; its primary competitors on the market are tadalafil (Cialis) and vardenafil (Levitra).

In April 2012 Avanafil (Stendra) is available also.

Read the articles about the excellent natural product Man Plus Power too.

What is Viagra used for?
This FDA approved prescription medicine is used to treat impotence in men. The product increases the body's ability to achieve and maintain an erection during sexual stimulation.
This drug does not protect you from getting sexually transmitted diseases, including HIV.

Who should not take the drug?
Men who are currently using medicines that contain nitrates, such as nitroglycerin should not use the drug because, taken together, they can lower the blood pressure too much.
The product should not be used by women or children.

General Precautions with Viagra:
You should have a complete medical history and exam to determine the cause of your impotence before taking the product. 
Men who have medical conditions that may cause a sustained erection such as sickle cell anemia, leukemia or multiple myeloma or who have an abnormally shaped penis may not be able to take the drug. 
There are several medications that are known to interact with the drug, so be sure to tell your doctor about all medications you are taking including those you can get without a prescription.  
The medicine has not been studied with other treatments for impotence, so use in combination with other treatments is
not recommended.
Viagra formula chimica

How should I take Viagra?
Your healthcare provider may prescribe the product as one tablet once a day, about 1 hour before sexual activity. However, the product may be taken anywhere from 30 minutes to 4 hours before sexual activity.

What are some possible side effects of Viagra?
(This list is NOT a complete list of side effects reported with the drug. Your healthcare provider can discuss with you a more complete list of side effects.)
The medicine is generally well tolerated. If any side effects are experienced, they are usually mild and temporary.
The following is a listing of the most common side effects:

Upset stomach
Stuffy nose
Urinary tract infection
Visual changes such as mild and temporary changes in
blue/green colors or increased sensitivity to light.

ViagraUsing Viagra with other Medicines
Always discuss with your health care practitioner ALL of the medications you are taking (prescription and over-the-counter). In that way, you can receive the best advice for your own situation.
At present, the drug is not recommended for people taking commonly prescribed short- and long-acting nitrates because the combination may lower blood pressure.

A list of commonly prescribed short- and long-acting nitrates available in the United States: Deponit, Minitran, Nitrek, Nitro-Bid,  Nitrocine,  Nitro-Derm,   Nitro Disc, Nitro-Dur,  Nitrogard, Nitroglycerin, Nitroglycerin T/R, Nitroglyn,  Nitrol Ointment,  Nitrolan,  Nitrolingual Spray,  Nitrong,   Nitropar,  Nitropress,  Nitroprex,  Nitro S.A.,  Nitrospan,   Nitrostat,  Nitro-Trans System, Nitro Transdermal,  Nitro-Time,  Transderm-Nitro,   Tridil, Isosorbide Mononitrate , Imdur,  ISMO,   Isosorbide Mononitrate,  Monoket, Isosorbide Nitrate, Dilatrate-SR,  Iso-bid, Isordil,  Isordil Tembids,  Isosorbide Dinitrate Isosorbide Dinitrate LA,  Sorbitrate,  Sorbitrate SA, Pentaerythritol Tetranitrate, Peritrate,  Peritrate SA, Erythrityl Tetranitrate, Cardilate, Isosorbide Dinitrate/Phenobarbital, Isordil w/PB, Illicit Substances Containing Organic Nitrates,  e.g., amyl nitrate or nitrite (It is known that amyl nitrate or nitrite is sometimes abused. In abused situations, amyl nitrate or nitrite may be known by various names, including "poppers.")

Keep Viagra where children cannot reach it. A locked cupboard at least 1 ฝ metres above the ground is a good place to store medicines.

Keep the drug in a cool, dry place where the temperature stays below 30บC.
Do not store it or any other medicine in the bathroom or near a sink.
Do not leave it in the car or on window sills. Heat and dampness can destroy some medicines.
Keep the tablets in their pack until it is time to take them.

If your doctor tells you to stop taking the product, or the tablets have passed their expiry date, ask you pharmacist what to do with any left over.
All strengths come in blister packs of 4.

Active ingredients
- sildenafil citrate 25mg
- sildenafil citrate 50mg
- sildenafil citrate 100mg

Other ingredients
- Microcrystalline cellulose
- Calcium hydrogen phosphate anhydrous
- Croscarmellose sodium
- Magnesium stearate
- Hypromellose
- Titanium dioxide (E171)
- Lactose
- Glycerol triacetate
- Indigo carmine aluminium lake (E132)
- PF0102
Name                Dosage                  Time before it starts to act               How to take                                             Fatty food/alcohol             Effect lasts
Viagra 50mg, 100mg 1 hour take with a glass of water no 3-4 hours
Viagra Soft 50mg, 100mg 15 - 20 minutes put under the tongue till it dissolves yes 6 hours
Cialis 20mg 30 minutes take with a glass of water no 36 hours
Cialis Soft 20mg 15 - 20 minutes put under the tongue till it dissolves yes 24 - 36 hours
Levitra 20mg 10 minutes - 1 hour take with a glass of water no 12 hours

The mechanism of action of Sildenafil citrate involves the release of nitric oxide (NO) in the corpus cavernosum of the penis.

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.

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.

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. O

ther drugs that operate by the same mechanism include tadalafil (Cialis) and vardenafil (Levitra).

Sildenafil is metabolised by liver enzymes and excreted by both the liver and kidneys.

If taken with a high-fat meal, absorption is reduced; the time taken to reach the maximum plasma concentration increases by around one hour, and the maximum concentration itself is decreased by nearly one-third.

The primary indication of sildenafil is treatment of erectile dysfunction (inability to sustain a satisfactory erection to complete intercourse). It use is now standard treatment for erectile dysfunction in all settings, including diabetes.

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 improved sexual function in men in this situation.

Following up to earlier reports from 1999, the same researchers found that sildenafil was able to improve sexual function in female patients on antidepressants as well.

Professional sports players have been using drugs such as Viagra thinking that the opening of their blood vessels will enrich their muscles, therefore enhancing their performance.

Viagra's popularity with young adults has increased over the years.

It is sometimes used recreationally, though this use is somewhat pointless in young, healthy men, as they receive no benefit from the drug.

Some users mix Viagra with methylenedioxymethamphetamine (MDMA, ecstasy) or other stimulants 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'." Mixing with amyl nitrite is particularly dangerous, and is potentially fatal.

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.

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 aids jet lag recovery in hamsters. Their research was published in the Proceedings of the National Academy of Sciences.


Viagra Pfizer 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. 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.


Contraindications include:

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

  • 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)


In clinical trials, the most common adverse effects of sildenafil use included headache, flushing, dyspepsia, nasal congestion and impaired vision, including photophobia and blurred vision.

Some sildenafil users have complained of seeing everything tinted blue (cyanopsia).

Some complained of blurriness and loss of peripheral vision. In July 2005, the U.S. Food and Drug Administration found that sildenafil could lead to vision impairment in rare cases and a number of studies have linked sildenafil use with nonarteritic anterior ischemic optic neuropathy.

Rare but serious adverse effects found through postmarketing surveillance include priapism, severe hypotension, myocardial infarction (heart attack), ventricular arrhythmias, stroke, increased intraocular pressure and sudden hearing loss.

As a result of these postmarketing reports, in October 2007, the FDA announced that the labeling for all PDE5 inhibitors, including sildenafil, required a more prominent warning of the potential risk of sudden hearing loss.


Sildenafil (compound UK-92,480) was synthesized by a group of pharmaceutical chemists working at Pfizer's Sandwich, Kent, research facility in England.

It was initially studied for use in hypertension (high blood pressure) and angina pectoris (a symptom of ischaemic heart disease).

The first clinical trials were conducted in Morriston Hospital in Swansea.

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.

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 US Food and Drug Administration on March 27, 1998, becoming the first oral treatment approved to treat erectile dysfunction in the United States, and offered for sale in the United States later that year.

It soon became a great success: annual sales of Viagra in the period 1999–2001 exceeded $1 billion!

The British press portrayed Peter Dunn and Albert Wood as the inventors of the drug, a claim which Pfizer disputes. 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 soccer star Pel้).

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 2000, Viagra sales accounted for 92 percent of the global market for prescribed erectile dysfunction pills.

By 2007, Viagra's global share had plunged to about 50 percent due to several factors, including the entry of Cialis and Levitra, along with several other counterfeits and clones, and reports of vision loss in people taking PDE5 inhibitors.

In February 2007, it was announced that Boots the Chemist would trial over the counter sales of Viagra in stores in Manchester, England.

Men aged between 30 and 65 would be eligible to buy four tablets after a consultation with a pharmacist.

Pfizer's worldwide patents on sildenafil citrate will expire in 2011–2013.

The UK patent held by Pfizer on the use of PDE5 inhibitors as treatment of impotence was invalidated in 2000 because of obviousness; this decision was upheld on appeal in 2002.


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.
  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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You have to consult your doctor before the beginning of any treatment program


Nitric oxide or nitrogen monoxide.

It is a stable free radical. According to Dr. Proctor, the NO  is the natural form of minoxidil (the minoxidil imitates the NO) and the natural modulator of the growth of the hair.

It seems to have a great importance for the human body, and not only for hair growth.

It is in fact a "signal" molecule . The nitroxide is the base of Viagra.

Besides it is mio-relaxant, it inhibits the aggregation of the plaques, acts on the cardiovascular system dilating the artery, so good for the erection and the release of the GH.

In 1977 Ferid Murad, MD, studying the mechanism  of the nitroglycerine, discovered that it acted releasing NO, which relaxes the cells of the smooth musculature.

In 1980 the prize nobel Dr. Robert Furchgott denominated this molecule signal endothelium derived relaxing factor (EDFR).

In 1986 Louis J. Ignarro discovered that EDRF and NO  are the same thing.

The precursor in the human body is arginine.

Here are some types of nitroxides:



Treatment of the induced alopecia  by radiations with topical applications of nitroxide.
The active mechanism in the growth of the hair

U.S. Food and Drug Administration

  • FDA Talk Paper
  • Questions and Answers
  • Consumer Drug Information Sheet
  • MedicineNet Erectile Dysfunction

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