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History of sildenafil citrate.
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Sildenafil citrate, also known as Viagra, Revatio and saome other trade names, is a drug used to heal erectile dysfunction and pulmonary arterial hypertension. It was created and is sold by the pharmaceutical company Pfizer. Its action is made by inhibiting cGMP specific phosphodiesterase type 5, an enzyme that regulates blood flow in the penis. Viagra was sold from 1998, sildenafil has been the prime treatment for erectile dysfunction; its competitors on the market are tadalafil (Cialis) and vardenafil (Levitra). It is frequently called the ‘blue pill’.
History
Sildenafil (compound UK-92,480) was synthesized by group of chemists working at Pfizer’s Sandwich, Kent, in England. It was initially studied for use in hypertension (high blood pressure) and angina pectoris (a symptom of ischaemic heart disease). The first clinical trials were made in Morriston Hospital in Swansea.[1] First phase clinical trials under the direction of Ian Osterloh suggested that the drug had small effect on angina, but that it could induce marked penile erections. So Phitzer decided to market it for erectile dysfunction, than for angina. The drug was patented in 1996, approved for use in erectile dysfunction by the US Food and Drug Administration on March 27, 1998, becoming the first oral treatment approved to treat erectile dysfunction in the United States, and offered for sale in the United States later that year.[4] It soon became a great success: annual sales of Viagra in the period 1999–2001 exceeded $1 billion.[citation needed]
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.buy viagra
Even though sildenafil is available only 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 soccer star Pelé). Numerous sites on the Internet offer Viagra for sale after an “online consultation”, often a simple 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.[6]
In 2000, Viagra sales accounted for 92 percent of the global market for prescribed erectile dysfunction pills.[7] By 2007, Viagra’s global share had plunged to about 50 percent[8] due to several factors, including the entry of Cialis and Levitra, along with several other counterfeits and clones, and reports of vision loss in people taking PDE5 inhibitors.
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.
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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