There are no real
long term studies available on the products. According to Schwarz, “The
only issue is that the data we have are from relatively short-term
studies. Viagra has been on the market since 1998 and the other two
PDE-5 inhibitors were approved by the FDA in 2003. Therefore, we do not
have multi-year follow-up studies. On the other hand, the drugs have
been on the market for several years now and there have been no reports
of negative long-term effects.”
Recently the Food
and Drug Administration (FDA) approved a reformulation of sildenafil
(Viagra) for the treatment of primary pulmonary hypertension, a disease
that tends to occur in young women, causing elevated blood pressures in
the lung that can lead to heart failure and early death.
There are
differences in the three medications, but they all limit the activity of
the enzyme phosphodiesterase-5 (PDE-5), which is found in tissues and
vessels of the penis, blood platelets, and smooth muscle of blood
vessels. The erectile dysfunction condition is solved when they
constrain the enzyme’s action which results in increased levels of
cyclic guanosine monophosphate (cGMP) and nitric oxide (NO),
biochemicals that promote smooth muscle relaxation and increased blood
flow in erectile tissue.
The researchers
say that PDE-5 inhibitors can be used to treat erectile “dysfunction
even for many men who also have diabetes, those who are older, and those
who have co-existing ischemic heart disease.” Since PDE-5 can smooth
muscles of the systemic arteries and veins throughout the body, the use
has been associated with various cardiovascular effects.
Schwarz says “The
original intention was to develop PDE-5 inhibitors as a treatment for
angina, chest pain that occurs when the heart is starved for oxygen.”
He added, “As such, their effects on the heart appear to be all
beneficial. Nitrates and other substances commonly used to improve blood
flow and oxygenation to the heart muscle have a side effect that we call
the ‘steal phenomenon,’ in which blood is taken away from underperfused
(flow-restricted) areas to improve blood flow in normal areas. In
contrast, PDE-5 inhibitors actually improve blood flow even in areas
where there is a blockage of an artery, thereby having a protective
effect on the heart muscle.”
There was some
concern with sight-loss (NAION or non-arteric anterior ischemic optic
neuropathy) in patients taking the drugs. But according to the
researchers, after an analysis of 13,000 men and more than 35,000
patient observations, they found the “occurrence of the visual disorder
to be similar to that of the general population.”
Among other
findings:
• Although the
enzyme PDE-5 has been found in tissue and arteries of the brain,
sildenafil does not appear to dilate cerebral arteries or have an effect
on cerebral blood flow or blood flow velocity, an indication that there
is no increased risk of stroke or hemorrhage.
• PDE-5 exists in
blood platelets, cells that play a major role in the blood clotting
process, but sildenafil appears to have no direct impact on platelet
function. However, the drug’s effects have not been specifically
evaluated in patients with bleeding disorders or in those taking drugs
that reduce clotting.
“Experimental and
human studies indicate that PDE-5 inhibitors are effective and well
tolerated, and there is evidence that they are not being used to their
utmost potential. We suggest that these drugs may prove beneficial in
treating a wide variety of disorders,” said Schwarz, the article’s first
author and a specialist in cardiology, interventional cardiology, heart
failure, and transplantation. “Some studies are underway to determine
the effects of long-term use of PDE-5 inhibitors, and others are
warranted, especially in patients who are considered at high risk
because of chronic cardiovascular disorders.”
Their findings
appear in the June 8, 2006 issue of the International Journal of
Impotence Research.
Dan Wilson
Best Syndication
Books on Heart Disease
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