What is Generic Viagra
Viagra is the brand name for sildenafil citrate and used for the treatment of erectile disfunction, otherwise known as male impotence. Generic Viagra is the same Sildenafil Citrate but marketed under different brand names and often at lower prices. Generic versions of brand name drugs have existed for a long time, but the generic version of Viagra is relatively new and brings new possibilites for affordable impotence treatment. You can expect generic Viagra to work in the same way as brand name Viagra because they contain the exact same active ingredient (Sildenafil Citrate). If Viagra is safe for you (as decided by your doctor) Generic Viagra is also safe for you and should be taken in the same doses as prescribed by your doctor.

How Does Viagra Work
When sexual stimulation begins nitric oxide (NO) is released into the spongy tissue of the penis. NO then activates an enzyme that increases the production of cyclic guanosine monophosphate (cGMP) the substance that relaxes the spongy tissue of the penis and facilitates an influx of blood. As specific enzymes slowly degrade cGMP the penis will slowly loose its ability to sustain an erection. Viagra works by inhibiting those enzymes that degrade cGMP, thereby enhancing ones ability to obtain and sustain an erection. VIAGRA enables many men with erectile dysfunction to respond to sexual stimulation. When a man is sexually excited, VIAGRA helps the penis fill with enough blood to cause an erection. After sex is over, the erection goes away.

How Effective is Viagra
Over 21 studies have been done to evaluate the efficacy of Viagra. Evaluation of drug activity was most often done using a self-assessment questionnaire. During a 6-month open labeled study, Viagra was found to improve sexual function in 88% of those treated. This included frequency, firmness, and maintenance of an erection; frequency of orgasm; frequency and level of desire; frequency, satisfaction and enjoyment of sexual intercourse; and overall relationship satisfaction.

History
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 form of ischaemic cardiovascular disease). 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 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. 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 by prescription from a doctor, it was advertised directly to consumers on US TV (famously being endorsed by former United States Senator Bob Dole and football star Pelé). Numerous sites on the Internet offer Viagra for sale after an “online consultation”, a mere 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. 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.
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. 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) in the corpus cavernosum, 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. Other drugs that operate by the same mechanism include tadalafil (Cialis®) and vardenafil (Levitra®).

Sildenafil is metabolised by hepatic enzymes and excreted by both the liver and kidneys. 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. The dose of sildenafil is 25 mg to 100 mg taken once per day between 30 minutes and 4 hours prior to sexual intercourse.

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.

Viagra pills are blue and diamond-shaped with the words “Pfizer” on one side, and “VGR xx” (where xx stands for “25″, “50″ or “100″, the dose of that pill in milligrams) on the other.
Contraindications
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)

Viagra side effects
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of Viagra.

Stop using Viagra and call your doctor at once if you have any of these serious side effects:

*sudden vision loss;
*chest pain or heavy feeling, pain spreading to the arm or shoulder, nausea, sweating, general ill feeling;
*irregular heartbeat;
*swelling in your hands, ankles, or feet;
*shortness of breath;
*vision changes;
*feeling light-headed, fainting; or
* penis erection that is painful or lasts 4 hours or longer.

Less serious side effects may include:

*warmth or redness in your face, neck, or chest;
*stuffy nose;
*headache;
*upset stomach; or
*back pain.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.

Absorption, Bioavailability

Viagra is rapidly absorbed. Maximum observed plasma concentrations
of Viagra are reached within 30 to 120 minutes (median 60 minutes) of
oral dosing in the fasted state. Viagra is about 40% biovailable. Viagra
is highly protein bound (96%). When Viagra is taken with a high fat
meal, the rate of absorption is reduced.

Metabolism, Half Life, Excretion

Viagra is mostly metabolized in the liver by an enzyme known as
CYP3A4 and to a lesser extent CYPC229. Viagra breakdown products
are excreted in the feces (80%) and in the urine (approximately 13%). Viagra’s mean half life is about 4 hours.

If you are going to take any of the PDE5 inhibitors such as Viagra, it is
very important that your doctor be aware if you have a liver condition
(such as cirrhosis) or kidney condition ( such as if you are on dialysis)
because you may need a special dosage adjustment.

Likewise, if you try to obtain Viagra on the internet, please make sure
that the person authorizing your prescription knows the true status of
your liver function and your kidney function.