Study shows life-threatening link between Viagra and nitrates and recommends guidelines for safe use

A study published in tomorrow’s edition of Circulation reports that sildenafil citrate (Viagra), when combined with nitrates, can cause serious and prolonged decreases in blood flow through critically narrowed coronary arteries.

Researchers at Osaka University, Osaka, Japan and Mayo Clinic monitored changes in blood pressure and blood flow through coronary arteries in animals given nitrate along with the doses of Viagra achieving similar blood levels as prescribed for erectile dysfunction. They believe the study shows a possible cause for the sudden deaths that have been reported among men using Viagra.

"We found that Viagra, when combined with nitrates, causes a prolonged reduction in blood flow to the heart in critically narrowed coronary arteries," says Bijoy Khandheria, M.D., a Mayo Clinic cardiologist and one of the study authors. "The good news is that Viagra alone did not significantly decrease blood flow through narrowed arteries. In normal vessels, it actually increased blood flow. The negative effect came only when it was combined with nitrates."

In addition to highlighting the need for patients to only take Viagra under medical supervision, Dr. Khandheria says the findings provide important guidance for physicians in how to prescribe Viagra safely. "Many heart patients need to take nitrates, and many want to use Viagra. This study shows that they should not be taken together. The old adage of taking a nitroglycerine tablet prior to sexual intercourse falls by the wayside if Viagra is prescribed, since the combination can be lethal."

Doctors prescribe nitrates in various forms to relieve or prevent chest pain, known as angina. Common forms include nitroglycerine tablets placed under the tongue, sprays, patches or long-acting tablets. Dr. Khandheria says understanding the interaction with Viagra is important because so many heart patients also experience erectile dysfunction.

"Men being treated for heart disease are several times more likely to experience moderate or complete impotence, compared with other men their age," says Dr. Khandheria. "As a result, many heart patients are interested in using Viagra to maintain their quality of life, so we need to know how it interacts with other medications they may be taking. This study shows a potentially life-threatening interaction between Viagra and nitrates.

"Based on our study, we strongly suspect that a death would be induced by a vicious circle," says Dr. Khandheria. "The two drugs interact to reduce blood flow in arteries with critical stenosis, causing a drop in blood pressure, which deprives the heart of oxygen. The weakened heart further decreases blood pressure, and the downward spiral continues."