Viagra's discovery as an impotence therapy was a happy accident. The manufacturer Pfizer Inc. initially tested the drug as a heart medicine. It turned out to be ineffective for that use, but many of the participants in the study noted a surprising side effect. Men who were impotent were able to have erections.
Before the drug was approved by the Food and Drug Administration in March,1998 studies were conducted on 4,000 men with erectile dysfunction, caused by a variety of medical as well as psychological conditions. Results showed that 64 percent to 72 percent completed intercourse after taking Viagra, compared with 23 percent of men taking a dummy pill. Men were instructed to take the drug about an hour before intercourse.
Common side effects include flushing in the face, headache and upset stomach. Some men reported a blue tinge to their vision while taking the drug. Men are warned not to take Viagra if they are also taking nitrate heart drugs, such as nitroglycerin.
The drug, which goes by the generic name sildenafil citrate, works by causing the release of a chemical found largely in the penis, cyclic guanosine monophosphate (cyclic GMP), that in turn causes the smooth muscle of the penis to relax, allowing the organ to fill with blood and become erect. The drug also suppresses an enzyme that breaks down cyclic GMP, extending the duration of erection.
Viagra is not the only treatment for impotence, though it is the first effective oral medication. Other therapies include drugs that can be injected or inserted directly into the penis. Another oral medication, apomorphine, is being tested and could be available in about a year.
Reference: The Washington Post Company, 1998
Origin: 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 symptom of ischaemic heart disease). The first clinical trials were conducted in Morriston Hospital in Swansea. 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 United States 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. It soon became a great success: annual sales of Viagra peaked in 2008 at US$1,934 million.
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