Side-Effects From Erectile Dysfunction Drugs Mostly Beneficial, Says Study

19 June 2006
Side-Effects From Erectile Dysfunction Drugs Mostly Beneficial, Says Study
by George Atkinson

The enormous success of drugs like Viagra (sildenafil) has been clouded somewhat by studies that have suggested it may be linked to a number of serious side-effects such as optic nerve damage, nosebleeds and stroke. But now, a review of past studies into side-effects from erectile dysfunction drugs by Ernst R. Schwarz, at Cedars-Sinai Medical Center, has found that the drugs (called phosphodiesterase-5 inhibitors: PDE-5 drugs include Viagra, Levitra and Cialis), produce mostly beneficial results, and not just for erectile dysfunction. The findings by Schwarz and his colleagues appear in the International Journal of Impotence Research.

"[Looking] at all the different organ systems - the blood, the heart, the lungs, blood flow in the brain - there are hardly any negative side effects. In fact, just the opposite is true. There are beneficial effects for primary pulmonary hypertension, as well as for conditions such as heart failure and lack of oxygen in the heart," said 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."

The researchers said that while there were some differences among the three medications; they had many properties in common, working by limiting the activity of the enzyme phosphodiesterase-5, which is found in tissues and vessels of the penis, blood platelets, and smooth muscle of blood vessels. For the treatment of erectile dysfunction, the drugs' constraint of the enzyme's action 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 study found that PDE-5 inhibitors can be effective in treating erectile dysfunction; even for those men who have diabetes, those who are older, and those who have co-existing reduced blood flow to the heart caused by plaque buildup in the arteries. "Since PDE-5 is found in smooth muscles of the systemic arteries and veins throughout the body, use of PDE-5i has been associated with various cardiovascular effects. 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," Schwarz explained. "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."

Whether erectile drugs might cause damage to the optic nerve was a matter of controversy when a suspected link between PDE-5 inhibitors and vision loss led to lawsuits filed last year against the maker of Viagra. According to the article's authors, however, "analysis of clinical trial data in more than 13,000 men and on more than 35,000 patient-years of observation" found occurrence of the visual disorder to be similar to that of the general population. "Even though individual cases have been reported for all PDE-5i, these recently published data do not suggest an increased incidence of non-arteric anterior ischemic optic neuropathy in men who took PDE-5 for ED," said the researchers.

Stroke was another bogeyman that the researchers laid to rest. Stating that, 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. All up (no pun intended), erectile drugs got a glowing report from the researchers. "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 [non-erectile dysfunction] disorders," concluded Schwarz.

Based on material from the Cedars-Sinai Medical Center