Sildenafil citrate, marketed as Viagra® was approved as a drug for treating male erectile dysfunction (ED) by the US Food and Drug Administration on 27 March 1998. The release of this drug on the world market had a very large impact as could be judged by the attention it was given by the media. This was due to the fact that the drug was a breakthrough for men suffering from ED. They represent a significant part of the male population : it is estimated that 10% of men suffer from erectile dysfunction, and that this figure is as much as 52% for men between 40 and 70 years old.

Viagra was discovered by a research team in the Pfizer Sandwich site in Kent. It was first reported in the Bioorganic & Medicinal Chemistry Letters in 1996 in which its synthetic pathway was published. The Pfizer research team started working on the programme in 1985 with the aim of discovering antihypertensive and antianginal compounds. They were studying compounds which inhibit phosphodiesterase (PDE), including Zaprinast which had already been reported but wasn't selective enough and hadn't been commercialised. At that point, the researchers had no idea that their research would lead them to discover an anti-impotence drug. In 1989 Sildenafil had been synthesised. Clinical trials of sildenafil were started in July 1991. In 1992, the researchers realised that the drug was not as effective as they had hoped. However, they were surprised because many of the patients that had tried sildenafil were reluctant to stop the trial, and wanted to continue taking the drug. The researchers finally learnt from some of the patients that one of the side effects of the drug was that it helped erection.

The team then decided to change course and put the new molecule, sildenafil, on trial as a drug for erectile dysfunction. The clinical trial for sildenafil as a drug for ED started in May 1994. It was a limited trial but the results were very encouraging and further tests were started. In total, 3,000 patients aged 19 to 87 years were treated with Viagra over a period of 5 years. Improvement in erection was demonstrated to be statistically significant, for erectile dysfunction of different etiologies (organic, psychogenic and mixed).
The development of this drug gave hope to many men, and was an instant success when it was administered by medicinal doctors for the first time in the USA. Today in Britain Viagra is not yet available on the NHS, however it can be purchased. The success of Viagra could be measured just by judging by the number of sites on the internet from which the drug could be bought. It is however still quite expensive to buy, and and it is therefore not at all available for everyone to use.
Pfizer has also undertaken researches on the effect of Viagra on women, although the results are not known yet and will not be discussed here. Apparently, the drug could have some benefits in augmenting sexual functioning in women. Since Viagra increases blood flow, it might help some women with lubrication and arousal. These studies have only just begun, and therefore nothing is known about this subject yet.

This webpage was written by Pascale Hazel
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