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Sildenafil
citrate, sold under the names Viagra, Revatio and under various
other names, is a drug used to treat male erectile dysfunction
(impotence) and pulmonary arterial hypertension (PAH), developed
by the pharmaceutical company Pfizer. Its primary competitors
on the market are tadalafil (Cialis), and vardenafil (Levitra).
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.[5]
Pfizer's worldwide patents on sildenafil citrate will expire
in 2011–2013. The UK patent held by Pfizer on the use
of PDE5 inhibitors (see below) as treatment of impotence was
invalidated in 2000 because of obviousness; this decision was
upheld on appeal in 2002.
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