Sildenafil Citrate is a popular drug, with the brand name Viagra or Revatio, used for the treatment of erectile dysfunction and pulmonary arterial hypertensions. Viagra, a trademark drug of Pfizer is a blue-colored, diamond shaped pill with the word "Pfizer" on one side and the letters "VGR xx" on the other side written on it. The letters VGR xx stands for the doses of the pill in milligrams, 25, g50 and 100 respectively. Viagra is available under different other brand names too.

Sildenafil Citrate, the main ingredient of Viagra belongs to a class of drugs called phosphodiesterase (PDE) inhibitors that works by enhancing the rate of the flow of blood to the penile region during sexual stimulation.

The Systematic (IUPAC) name of Sildenafil is 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. Its chemical formula is C22H30N6O4S.

Let us discern how Sildenafil Citrate helps an ED patient to attain an erection:

The physiological mechanism of penile erection involves the release of nitric oxide (NO) in the corpus cavernosum region of the penis during sexual stimulation. The nitric oxide stimulates the enzyme, guanylate cyclase, which enhances the cyclic guanosine monophosphate (cGMP) level and produce smooth muscle relaxation in the corpus cavernosum. It allows an increased inflow of blood in the penis.

Sildenafil Citrate, the main component of Viagra is seen to have no direct relaxing effect on the isolated human corpus cavernosum, but it greatly improves the effect of nitric oxide (NO) by inhibiting phosphodiesterase type 5 (PDE5), which generally degrades the cGMP in the corpus cavernosum. When nitric oxide is released due to sexual stimulation, Sildenafil inhibits the PDE5 and enhances the levels of cGMP in the corpus cavernosum, ensuing smooth muscle relaxation and higher rate of the inflow of blood to the corpus cavernosum, producing erection.

Remember the following facts of Viagra, before you start using it as a treatment for erectile dysfunction or impotence:

• Viagra or Sildenafil is an oral drug
• Viagra or Sildenafil is not a magic pill, a person has to be sexually stimulated for this drug to work
• Viagra or Sildenafil should be taken only once in 24 hours
• Viagra or Sildenafil is not an aphrodisiac, it cannot increase your sexual desire
• Viagra or Sildenafil cannot prevent pregnancy
• Viagra or Sildenafil cannot protect you from STDs or HIV/AIDS
• Viagra or Sildenafil does not cure erectile dysfunction
• Viagra or Sildenafil should be used only under the supervision of a registered physician