CONTACT: DAVE PEDERSEN
Iowa City IA 52242
(319) 335-8032; fax(319) 335-8034
Release: Jan. 3, 2001
UI study finds Viagra increases nerve activity associated with cardiovascular
IOWA CITY, Iowa The drug sildenafil citrate better known as
Viagra causes a dramatic increase in the nerve activity associated
with cardiovascular function, especially during physical and mental stress,
bolstering recommendations that men with severe cardiovascular disease use
caution when taking the drug.
This finding comes from researchers at University of Iowa Cardiovascular
Research Center who studied the effect of Viagra on the cardiovascular system
at rest and during stressful conditions. The results are published in the
Dec. 19 issue of the journal Circulation.
"Little is known about Viagra's effect on the cardiovascular system,
particularly during situations when the cardiovascular system is under stress,
as it is during sexual activity," said
Bradley G. Phillips, Pharm.D., assistant professor in the UI College of Pharmacy.
"Recent concern and reports of heart attacks, arrhythmias and even deaths
temporally related to Viagra use in patients with heart failure initially
raised questions about the drug's effect on the cardiovascular system."
Phillips and other investigators, including Virend Somers, M.D., Ph.D., and
Catherine Pesek, D.O., from the UI department of internal medicine, conducted
the study. Somers is now a researcher at the Mayo Clinic.
The researchers studied 14 healthy men, ages 25 to 39, who were given a 100-milligram
dose of Viagra or placebo on two separate study days. Men who received Viagra
on the first study visit were given placebo on their second visit and vice-versa.
Neither the participants nor the researchers knew which drugs were being administered
on either of the study days.
The researchers took baseline measurements of the subjects' blood pressure
rates, heart rates, noradrenaline levels and sympathetic nerve activity (nerve
activity that causes blood vessels to constrict). The investigators took similar
measurements 30 and 60 minutes after administering Viagra and placebo while
study subjects rested. Immediately following the 60-minute "rest"
period, each participant's cardiovascular response was evaluated during stressful
conditions, including exercise, mental stress and cold exposure.
Compared to placebo, the researchers found that Viagra resulted in more than
a doubling of sympathetic nerve activity and a 30 percent increase in blood
levels of noradrenaline. Moreover, they found that sympathetic nerve activity
after Viagra increased even more dramatically during stressful conditions.
"It is well recognized that sympathetic nerve activity is already increased
in patients with cardiovascular diseases like heart failure and that this
high sympathetic activity is detrimental over the long term," Phillips
said. "Our study showed that Viagra increases this type of nerve activity
at rest and even further during stressful situations. For people with unstable
cardiovascular disease, this could be a problem."
The U.S. Food and Drug Administration approved Viagra in March 1998 as the
first oral pill to treat erectile dysfunction, a condition that affects millions
of men in the United States and as many as 100 million men worldwide. Phillips
noted that the study findings reinforce recommendations from the American
Heart Association and the American College of Cardiology that people with
cardiovascular disease should avoid using Viagra. Viagra also should not be
combined with other drugs, such as nitrates, Phillips added.