When doctors want to view inside the body, they inject what is called contrast medium, chemicals that make the blood vessels stand out in the images produced by X-rays and other imaging techniques. But contrast-medium-induced kidney damage has emerged as a major problem, sometimes leading to death.
"It is becoming one of the most common causes of acute kidney failure," said Dr. Michael Rudnick, associate professor of medicine at the University of Pennsylvania, who has done extensive research on the subject but was not part of the new study. "The only two more common causes are dehydration or low blood pressure," he said.
The Italian study, published in the June 29 issue of the New England Journal of Medicine, is the latest in a series of trials to test the value of acetylcysteine against kidney damage caused by contrast medium. That treatment became the subject of intense research after a German physician reported impressive results with the molecule in 2001.
"Since then, another 25 studies have looked at this," Rudnick said. "Half found no benefit. If you add up all the studies, you find a small reduction in risk which is not statistically significant," he added.
The Italian study, done at the University of Milan, included 354 patients who underwent the artery-opening procedure called angioplasty after having heart attacks. One-third of them were not given acetylcysteine; one-third got what the doctors called a standard dose, a 600-milligram intravenous injection before the procedure and 2,400 milligrams in the following two days; and the other third got twice that dose.
Kidney function is tested by measuring blood levels of creatinine, a breakdown product of creatine, which is an important part of muscle. Creatinine levels go up as kidney function goes down.
Among study participants, creatinine levels increased in 33 percent of patients who did not get acetylcysteine, in 15 percent of those getting the standard dose and in 8 percent of those who got the double dose, the researchers reported.
And 13 of those patients not getting acetylcysteine died in the hospital, while the death rate was lower for those who got the medication -- five of those getting the standard dose and three of those getting the larger dose.
While those numbers appear convincing, Rudnick found flaws with the study. Contrast-induced kidney failure is a problem primarily for people who already have reduced kidney function, he said, but 224 of the 354 people in the study had normal kidney function. "That is a pretty significant limitation," he said.
And the study did not meet the recommended rule of having the doctors blinded to which patients got which treatment, Rudnick said. That could introduce a subtle bias, he said.
"I don't think their data support routine use of this treatment," Rudnick said. "This should not become the standard of care based on this one study," he added.
The researchers apparently agreed with that assessment. "Further data are needed before any conclusions can be made," they wrote.
The study got a warmer reception from Dr. Deepika Misra, an attending physician in cardiology at Beth Israel Medical Center in New York City, who said she now uses acetylcysteine routinely in her practice.
"This is the kind of study needed to prove or disprove the value of this treatment," Misra said. "It was a very well done study, and it had enough patients to achieve the significance that they wanted."
But it was a special group of patients, Misra added, those undergoing emergency angioplasty for a heart attack, and so the use of acetylcysteine for other patients "remains to be looked at."