* Contrast dye used in heart X-rays can harm kidneys
* Drug acetylcysteine fails to shield kidneys from dye (Adds comments from researcher)
By Susan Kelly
CHICAGO, Nov 16 (Reuters) - A drug used to protect the kidneys from contrast dye during X-rays of the heart's blood vessels does not work, researchers said on Tuesday, citing a large study that may change the way patients are treated.
The widely available generic drug, acetylcysteine, is made by various companies around the world and marketed under numerous names.
Contrast dye used during coronary arteriograms and angiography procedures may harm kidney function in some patients, especially those older than 70 years and who have had kidney failure, congestive heart failure or diabetes.
"Some patients need this type of exam to diagnose if they need revascularization, but it's not good enough to fix the heart if it harms the kidneys," said Dr. Otavio Berwanger, lead author of the study and director of the Research Institute at the Hospital do Coracao in Sao Paulo, Brazil.
Damage from contrast dye is the second-most common cause of kidney failure in hospitals in Brazil and the third leading cause of kidney failure in U.S. hospitals.
In earlier studies, researchers found mixed results on the benefits of using acetylcysteine, a relatively safe and cheap medicine, to shield the kidneys from the contrast dye.
In the ACT study of 2,308 patients, 13 percent of those who received acetylcysteine suffered kidney damage after a cardiac X-ray procedure in which dye was used. The rate of kidney damage in patients who took a placebo was also 13 percent.
Results were the same in the drug and placebo groups regardless of the type of dye used, the researchers said.
Dr. Brahmajee Nallamothu of the University of Michigan in Ann Arbor said the ACT study is the definitive clinical trial addressing the effectiveness of acetylcysteine for the prevention of kidney disease induced by a contrast agent.
"The ACT trial will diminish the use of acetylcysteine," Nallamothu said. There is no role for routine use of acetylcysteine."
Although about 45 clinical trials have been conducted on the drug over the years, most were very small, averaging 80 patients, Nallamothu noted.
The ACT study was funded by Brazil's Ministry of Health and released at the American Heart Association's annual meeting in Chicago.
"This will inform clinical practice," Berwanger said. "Sometimes you have something implemented in clinical practice that is not useful, even if it is safe and cheap."
The researcher said less toxic contrast dyes, or a different compound that can protect the kidneys from dye, are needed.
Researchers are also studying the potential of saline as well as bicarbonate to protect the kidneys. (Reporting by Susan Kelly; editing by Lisa Von Ahn and Andre Grenon)