Description of Sildenafil

Sildenafil citrate, which is commonly sold as Viagra, Revatio and under various other trade names, is a kind of drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH). It was first developed by British scientists and then brought to market by the US-based pharmaceutical company Pfizer. It works by inhibiting cGMP-specific phosphodiesterase type 5, an enzyme that promotes degradation of cGMP, which regulates blood flow in the penis. Since becoming available in 1998, sildenafil has been the prime treatment for erectile dysfunction; its primary competitors on the market are tadalafil and vardenafil.

Viagra pills are usually blue and diamond-shaped with the word "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.
The dosage for pulmonary arterial hypertension 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.

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