TUESDAY, March 25 (HealthDay News) -- One of the most common bowel-cleansing preparations used by people who are about to have a colonoscopy can trigger both acute kidney failure and long-term renal damage in otherwise healthy patients.

New research suggests the risks of oral sodium phosphate solution and tablets are rare but real, particularly for elderly patients.

"People should be very cautious in the use of these agents because of their potential of causing kidney damage," said study author Dr. Anand Khurana, of the department of nephrology with the Scott & White Clinic at Texas A&M University in Temple, Texas.

The findings were published in the March 24 issue of the Archives of Internal Medicine.

Another popular prescription colonoscopy preparation -- polyethylene glycol solutions (PEG) -- was not the subject of the current study and does not appear to be associated with similar risks.

In 2006, the U.S. Food and Drug Administration put a black-box warning on the oral sodium phosphate solution, recommending that it be "used with caution" among patients with impaired kidney function due to its high phosphate content. However, the latest finding extends that concern to patients with no previous history of kidney trouble.

According to the American Cancer Society, colorectal cancer ranks third in the United States in terms of cancer diagnoses among both men and women. The organization estimates that about 150,000 people will develop the disease this year alone.

Typically, a colonoscopy is recommended for men and women over the age of 50 every 10 years as an effective way to screen for small growths called polyps and other signs of colorectal cancer. Some high-risk groups are encouraged to begin undergoing screenings at an earlier age.

The procedure involves the insertion of a slender and flexible lighted tube, fitted with a video camera, throughout the entire colon. A sigmoidoscopy relies on a similar but shorter tube to examine just the lower colon. Medication ensures that most patients feel no pain, and the screening is usually conducted on an outpatient basis.

However, patients must refrain from eating solid foods the day before the procedure, while also ingesting a bowel-cleansing liquid to clear out the colon.

The phosphate solution and tablets have been the preparations of preference because of convenience, as they are available without a prescription and require less clear liquid consumption than the polyethylene glycol solution.

To examine risks associated with use of the phosphate solution and tablets, the authors analyzed kidney function among 268 patients at their clinic who had undergone either a colonoscopy or sigmoidoscopy between 1998 and 2005.

Most were white, with an average age of 68. Two-thirds were women, and none had a history of kidney disease. All the patients followed a standard dietary and phosphate solution prep the day prior to their screening.

Khurana and his team found that its use was associated with a 6 percent drop in kidney function six months later; that figure rose to 8 percent one year later.

"This magnitude of loss of kidney function is significant," said Khurana, who noted that patients undergo numerous colonoscopies over their lifetime, and normal kidney function loss is confined to about 1 percent per year among patients over 40.

Khurana pointed out that the safety risks he observed might ultimately be the result of patients simply not following manufacturer instructions to drink large amounts of clear liquid when consuming the preparation. Undetected chronic kidney disease among older patients undergoing colonoscopies might also play a role in the findings.

Nevertheless, "we believe that PEG preps are a safer option for patients" until further testing is done, he said.

Dr. Hemant K. Roy, an associate professor in the department of medicine at Evanston-Northwestern Healthcare in Illinois, described the findings as "quite alarming" in an accompanying editorial.

However, he stressed that warranted concerns about phosphate solutions should not discourage patients from undergoing colon cancer screening.

"Colonoscopies save lives," he stressed. "We know it works. So this should not dissuade people from doing one. I think we just need to be cautious about the type of preparation we use and who we give it to, so that an extraordinarily rare complication is avoided. And we have options, so there is a way to do that."

More information

For additional information on colonoscopies, visit the American Cancer Society.