Cheap drug protects against CT contrast-induced nephropathy

As the number of patients undergoing contrast-enhanced CT scans grows, so does the risk of contrast-induced nephropathy. What can physicians do to protect their patients from kidney damage? Ask them to pop an N-acetylcysteine pill before the exam, according to a study by University of Michigan Medical School researchers.

Contrast-induced nephropathy is the third most common cause of acute renal failure in hospitalized patients. The condition affects about one in 10 patients with normal renal function but could hit almost a third of those with preexisting renal impairment or chronic disease, according to studies published since the mid-1980s.

Reports blame a growing number of cases on the booming utilization of CT and image-guided procedures.

"Millions of people receive contrast agent each year, including most heart patients who have angioplasties and stents, as well as those having a CT scan. Contrast agent helps physicians see the things we need to see, but it also does pose a hazard to some people," said principal investigator Dr. Aine M. Kelly, an assistant professor of radiology at Michigan.

Kelly and colleagues performed a meta-analysis of data from 41 randomized controlled studies done between 1966 and 2006 that evaluated several kidney-protecting drugs. They found that patients who took N-acetylcysteine could avoid serious kidney damage caused by iodine-based contrast agents. The drug costs about 25¢ for a 500 mg dose and is available in most pharmacies.

The investigators also found the drug outperforms other medicines used for the same purpose. Findings were published in the Feb. 19 issue of the Annals of Internal Medicine.

The 41 studies assessed the renal protective properties of N-acetylcysteine, theophylline, fenoldopam, dopamine, iloprost, statin, furosemide, and mannitol. Findings showed that only N-acetylcysteine consistently prevented contrast-induced nephropathy. Theophylline, the second-best kidney-protecting drug, did not reduce risk significantly. Conversely, furosemide raised the risk of contrast-induced nephropathies. The other drugs had no effect.

The meta-analysis included only studies involving intravenous iodine-based contrast media that were compared with water or saline infusion as controls.

A prospective trial comparing N-acetylcysteine directly with other drugs should be conducted to validate findings, Kelly said. In the meantime, patients with impaired renal function should alert their physicians when they order a contrast-enhanced CT scan, angiogram, or angioplasty and make sure to take a tablet of N-acetylcysteine beforehand.

"N-acetylcysteine is quick, inexpensive, widely available, and poses no major side effects," Kelly said.

For more information from the Diagnostic Imaging archives:

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Nonionic contrast media prove safe in pediatric patients

Protocols help protect older patients from CT-induced kidney damage

Contrast-induced nephropathy: How high the risk?

Contradictory study results fuel controversy over contrast danger