Viagra (Sildenafil Citrate)
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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).
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.[1][2]
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.[3] 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.[4] 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 U.S. 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.
