October 19th, 2011
11:42 AM ET
Every weekday, a CNNHealth expert doctor answers a viewer question. On Wednesdays, it's Dr. Otis Brawley, chief medical officer at the American Cancer Society.
Asked by Rosamond, from Philadelphia
I have wet macular degeneration that is being "successfully" treated with Avastin. Please comment on reports of blindness related to this treatment. Many thanks!
Age-related macular degeneration, or AMD, is a deterioration of the center of the visual field, which is called the macula.
AMD is one of the leading causes of adult blindness and severe visual impairment. Other common causes of visual impairment in older adults are cataract, glaucoma and diabetic retinopathy.
There are two kinds of AMD. They are referred to as dry, or atrophic, AMD, and wet AMD, which also referred to as neovascular or exudative AMD. Dry AMD typically progresses slowly over many years and is less threatening to vision than wet AMD.
Often, dry AMD is monitored and not treated. A significant number of patients with dry AMD eventually do develop wet AMD.
Much effort has been put into developing a treatment for wet AMD. Two vascular endothelial growth factor inhibitors - which were initially developed as anti-cancer treatments - are now commonly used in the treatment of wet AMD.
VEGF is a protein found in all humans. Its function is to cause growth of blood vessels. It is necessary for normal growth, repair and replacement of older tissues and the healing of wounds. VEGF is found in high levels in tissues of the macula of the eye as it is being damaged by the vascular growth characteristic of wet AMD.
Well designed clinical studies have shown that ranibizumab, a recombinant humanized monoclonal antibody, significantly inhibits VEGF activity and benefits patients with wet AMD when injected directly into the eye. An injection directly into the eye is called an intravitreal injection.
One trial randomized 716 patients to 24 monthly injections with ranibizumab 0.3 mg, ranibizumab 0.5 mg, or sham injection into the eye. Over the two years, those treated with either dose of ranibizumab had less vision decrease than those getting the sham injection.
Some patients treated with the VEGF inhibitor actually had improved vision. Ranibizumab (trade name Lucentis) was approved for treatment of wet AMD by the U.S. Food and Drug Administration in 2006 at a dose of 0.5 mg by injection into the eye every month. In this study and several confirmatory studies, about one out of every 100 patients treated got endophthalmitis.
This is an inflammation of the internal parts of the eye due to chemical irritation caused by a high concentration of the drug. It often leads to blindness. The FDA also noted that there is a small increased risk of stroke and myocardial infarction with ranibizumab treatment.
Bevacizumab (trade name Avastin) is a VEGF inhibitor closely related to ranibizumab. Bevacizumab is FDA-approved in the United States as an intravenous infusion to treat colorectal cancer and is commonly used to treat metastatic breast cancer.
Bevacizumab is frequently used off label as an intravitreal treatment of wet AMD. Off-label use is legal in the U.S. and is commonly done in medicine. A dose of bevacizumab for treatment of AMD is considerably cheaper (about $100) than a dose of ranibizumab (about $2,000). While bevacizumab has not been FDA-approved for AMD, studies comparing intravitreal bevacizumab and ranibizumab found no difference in effectiveness.
The rate of serious side effects was slightly higher with bevacizumab than with ranibizumab (24% versus 19%).
Major side effects of these drugs when given into the eye included pneumonia and urinary tract infections, nausea, vomiting and some gastrointestinal bleeding. There were a few patients who had stroke and myocardial infarction.
The risk of endophthalmitis was the same with bevacizumab and ranibizumab. While intravitreal injection of bevacizumab and ranibizumab is the standard method of use today, intravenous administration of bevacizumab is also being studied in the treatment of AMD. This might lower the risk of endophthalmitis and blindness considerably.
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