Viagra, Cialis and Levitra are used to treat erectile dysfunction. Although there are subtle differences in the way they work, all block the actions of an enzyme called PDE5. By blocking the enzyme, these drugs change the blood flow into and out of the penis and enhance a man's ability to have and maintain an erection. These drugs have proven very popular. Viagra, for example, has been given to over 20 million men since it was introduced in 1998. Overall, all three drugs have proven to be quite safe and relatively free of side effects.
The Food and Drug Administration is currently investigating 43 reported cases of a rare eye condition known as NAION (non-arteritic ischemic optic neuropathy) associated with the use of the three drugs. NAION is thought to be caused by a sudden lack of blood flow to the eye, resulting in rapid blindness. Unfortunately the condition is not reversible.
There are up to 6,000 cases of NAION reported in the United States annually. The condition is seen in older adults. The risk factors include diabetes and heart disease. Erectile dysfunction is frequently seen in older men with diabetes and heart disease. Because of the overlap, it is difficult to determine if the drugs are the cause of the problem, or if it is the underlying disease. We have known for some time that the three drugs can cause visual disturbances, such as a blue tinge to objects and difficulty in distinguishing between blue and green. This side effect is different and unrelated to the problem of NAION.
Of the 43 cases reported, 38 were related to use of Viagra, four with use of Cialis and one with Levitra. In seven of the cases, blindness occurred within 36 hours of the person taking one of the drugs.
At the moment, all three drugs appear to be associated with NAION. Because they all work essentially the same way, no one drug will be more likely than the others to cause the problem. Even though there are more cases seen in men taking Viagra, that doesn't mean that the other drugs are less likely to cause the problem. All have the same potential based on the information we have at the moment.
All drugs have risks associated with their use. Drugs for erectile dysfunction are no exception. NAION is an unusual disease that is seen in men and women with diabetes and heart disease. There may be a link between the use of Viagra, Cialis and Levitra and NAION; but we need a great deal more information to be certain.
