Approved by the Food and Drug Administration (FDA) in 2004, pegaptanib (Macugen), may offer new hope to people who experience the worst form of age-related macular degeneration (AMD), a disease that robs up to 1 million Americans of their eyesight each year.
The drug appears to slow the vision loss caused by "wet" AMD, the most serious form, by reducing the abnormal growth of blood vessels within the eye-the cause of AMD, which is the leading cause of blindness in people older than 55.
These blood vessels can bleed, exude fluid and eventually form scar tissue that destroys central vision, explains Dr. Evangelos Gragoudas, director of retina services at the Massachusetts Eye and Ear Infirmary and a professor of ophthalmology at Harvard Medical School.
The Studies
In two major clinical trials that observed more than 1,200 AMD patients at 117 eye clinics worldwide, Gragoudas, the lead author, and his research team compared the effectiveness of various doses of Macugen with a placebo. The drug was administered via regular injections into the eye.
The researchers report a reduced risk of vision loss in a majority of the patients receiving Macugen compared with those taking a placebo. This slowing of vision impairment began as early as six weeks into the therapy, and continued through the duration of the studies.
The researchers measured patients' vision loss by counting the number of letters on a standard eye chart that became illegible to the patients over the course of the study.
A loss of 15 letters would be considered a moderate vision loss, while a loss of 50 letters or more the equivalent of six lines) would be considered severe.
Of the patients receiving 0.3 milligrams (mg) of Macugen, 70% lost fewer than 50 letters, compared with just 55% among the controls," who were receiving a placebo, Gragoudas says. "The group that received the drug did much better in every kind of endpoint that we looked at."
The Explanation
Macugen, part of the family of anti-angiogenesis drugs, slows the growth of new blood vessels by blocking the activity of vascular endothelial growth factor (VEGF) within the eye. "It prevents the growth of new vessels, and it also prevents exudation-the leakage of fluid which is very common in abnormal vessels," Gragoudas says. "Sometimes, even if the vessels themselves don't completely disappear or regress, the fact that the fluid is absorbed can have a good effect on the patient."
Macugen offers the promise of being a significant new therapy in a disease that relentlessly causes (the gradual loss of functioning vision in the elderly population" says Dr. Stanley Chang, chairman of ophthalmology at Columbia University. However, he stresses that more study is needed because 40% of the eyes studied in Gragoudas' research continued to deteriorate and to become legally blind within one year.
In addition, Macugen's success rate in reducing vision loss did not exceed that of photody namic laser therapy, the only other treatment currently approved for use, adds Dr. Frederick Ferris III of the National Eye Institute.
But Gragoudas counters that this laser technique "is only allowed in a small number of patients, because a lot of (AMD) subtypes can't be treated with photodynamic therapy." And because Macugen is a drug and not a surgical intervention, its success in slowing vision loss "starts early on and continues through the whole treatment.
"The bottom line is that this is the first antiangiogenic treatment that has been used for the eye," says Gragoudas, "and it certainly decreases the rate of visual loss."
