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Mystery of Viagra Deaths Unravels

Drug May Affect Blood Clotting in Unexpected Ways

WebMD Health News

Jan. 9, 2003 -- While looking into the intricacies of blood clotting, researchers stumbled on a finding that may explain the mysterious deaths of a small number of men who took the impotence drug Viagra. Researchers say the drug may actually encourage potentially dangerous blood clots to form in men with certain risk factors, such as hardening of the arteries.

Viagra was originally developed as a drug to fight heart disease -- thought to increase blood flow by opening up blood vessels and prevent blood clots. But researchers have now found that the popular impotence drug may do exactly the opposite -- encouraging blood-clotting cells known as platelets to clump together and form clots. Their study appears in the Jan. 10 issue of the journal Cell.

During their research, Xiaoping Du and colleagues discovered that the enzyme that Viagra affects in the body to improve erections -- called cGMP -- may be the cause behind the increase in blood clots. Du is associate professor of pharmacology at the University of Illinois at Chicago College of Medicine.

Viagra helps stimulate erections by increasing levels of cGMP -- which is also involved in blood clotting. Therefore, by increasing levels of cGMP, Viagra may actually increase the risk of blood clots, according to the researchers.

To check this theory, the researchers tested the effect of Viagra on platelets. Alone, Viagra had no effect. But when exposed to an environment that simulated an injured blood vessel -- as in hardening of the arteries -- Viagra caused the platelets to clump. This occurred even at levels well below that found in men taking Viagra.

That means that if someone with an already damaged blood vessel takes Viagra, this clotting action may be enough to cause problems, according to the researchers.

"Viagra, by itself, probably is not sufficient to cause a heart attack in healthy people, but our research suggests that it may present a risk for patients with preexisting conditions such as atherosclerosis," says Du, in a news release.

SOURCE: Cell, Jan. 10, 2003. News release, University of Illinois at Chicago.

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