Inexpensive Medication May Prevent Contrast-Induced Kidney Damage

Patients at risk for kidney damage from CT scanning may be able to avoid complications by taking a relatively inexpensive and available drug the day before the test.

Ruth C. Carlos, M.D., M.S. University of Michigan

A study from the University of Michigan Health System, published in the Feb. 19, 2008, issue of the Annals of Internal Medicine, reviewed data from 41 randomized and controlled studies that looked at a number of drugs that could potentially prevent contrast-induced nephropathy (CIN).

Mild to moderate kidney damage occurs in one in four high-risk patients and in one in 10 patients with normal kidneys who undergo CT scanning, said senior author Ruth C. Carlos, M.D., M.S. In particular, a number of articles in the literature detail how iodine-based contrast agents put some people at risk for renal damage. Dr. Carlos and colleagues looked at articles on ways to reduce the threat, specifically analyzing published reports on agents used to prevent CIN.

"We as radiologists have a responsibility to improve the quality and safety of the exams we conduct," said Dr. Carlos, an associate professor of radiology. Dr. Carlos also chairs the Health Services Policy & Research Subcommittee of the RSNA Scientific Program Committee.

N-acetylcysteine Significantly Cuts Damage Risk

Comparing N-acetylcysteine, theophylline, fenoldopam, dopamine, iloprost, statins, furosemide and mannitol, the researchers concluded, "N-acetylcysteine significantly decreased the risk for contrast-induced nephropathy compared with saline alone." An inexpensive drug commonly stocked by pharmacies, N-acetylcysteine is used to help clear mucus from the lungs of cystic fibrosis patients and help treat overdoses of acetaminophen.

While a lack of studies on some agents made it difficult to fully understand their true effects, Dr. Carlos said there was a great deal of information available on the use of N-acetylcysteine.

Not everyone who receives a CT scan needs to receive N-acetylcysteine, she said. "Physicians who refer patients for iodine-based contrast exams should consider this medication for the elderly and for those with tenuous renal function," she said.

The study suggests people with diabetes or heart failure are at greatest risk for problems with contrast agents and could gain the most by taking the kidney-protecting drug.

Primary Physician Must Be Involved

While N-acetylcysteine is inexpensive and relatively risk free, the patient's primary physician must be responsible for prescribing it, said Michael Bettmann, M.D. "For radiologists, it's tough to give N-acetylcysteine orally since we don't get to see the patient until the day of the procedure—we don't have contact with the patient 24 hours ahead of time," said Dr. Bettmann, who was not involved with the study.

Dr. Bettmann, a professor and vice-chair for interventional services in the Department of Radiology at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., is among the instructors of an RSNA 2008 refresher course addressing CIN (see sidebar). He said intravenous N-acetylcysteine could potentially be given a half-hour before the procedure. University of Michigan researchers did not look at intravenous N-acetylcysteine in this study, only the pill form.

Radiologists need to raise awareness of CIN by educating their colleagues in radiology, other clinical colleagues and patients about the problem and the potential solution, said Dr. Carlos. She recommended that hospitals institute a policy of administering N-acetylcysteine prior to CT scans for those patients with high creatinine levels, a sign of potential kidney problems. Patients who aren't sure if they have kidney problems should ask their physicians to order a blood test to check their creatinine levels before getting a scan, she said.

Radiologists also need to work with physicians beforehand, just as they would if a patient was allergic to a medication, Dr. Carlos added. "We need to do this because a patient will follow up with his or her regular physician, not the radiologist who conducted the exam," she said. "This is an important way we as radiologists can reintegrate ourselves into patient care."

Further Study Must Examine Risk from Intravenous Contrast

Dr. Bettmann praised the University of Michigan study as important but noted the many variables in dealing with CIN research. Most studies of CIN involve intracardiac or other intra-arterial administration of contrast, he said, with essentially all N-acetylcysteine studies looking at reduction of risk among those patients.

"Many people question whether the risk of CIN is actually the same when contrast is given intravenously, as for CT, and I don't think the meta-analysis really is able to address that risk specifically," said Dr. Bettmann. "Although it is pretty clear that N-acetylcysteine helps for intracardiac/intra-arterial contrast, it remains to be proven both that there is a comparable risk of CIN with intravenous contrast and that N-acetylcysteine helps in that group.

"This is crucial for radiologists, since most of the contrast we give is intravenous," Dr. Bettmann continued. "We assume that the risk is the same and the benefit of N-acetylcysteine is the same, and they probably are, but as yet we have no proof."