The results of a study published in this week’s Archives of Internal Medicine reveal that oral sodium phosphate solution (OSPS) bowel preparation for colonoscopy should not be used in elderly patients even if creatinine levels are in the normal range. It seems that the solution may cause acute kidney failure and long-term renal damage. “Oral sodium phosphate solution preparations are preferred cleansing agents for colonoscopy because of ease of use and excellent preparation quality,” wrote Anand Khurana, MD, from Texas A&M University in Temple, and colleagues. “Besides causing acute renal failure in some patients, the high phosphorus content can potentially cause chronic kidney damage to patients undergoing colonoscopy.” OSPS is one of the most common bowel-cleansing preparations and the new research suggests the risks of OSPS and tablets are rare but real, particularly for the elderly.
The study looked at 286 patients with creatinine levels in the normal range who underwent colonoscopy or sigmoidoscopy with use of OSPS preparation. Most patients were white with an average age of 68; 2/3 were women and none had a history of kidney disease. All followed a standard dietary and phosphate solution preparation the day before the procedure. The study ran from 1998 to 2005 and was followed up for one year to determine effects on renal function. Patients were compared with a control group of 125 patients. Although both groups had similar baseline characteristics, they had significantly different renal function at six months. In an accompanying editorial, Hemant K. Roy, MD, from Feinberg School of Medicine, Evanston-Northwestern Healthcare in Evanston, Illinois, and Laura K. Bianchi, MD, call these findings “alarming,” although they need confirmation. Khurana and his team found that its use was associated with a six percent drop in kidney function six months later; that figure rose to eight percent one year later. “This magnitude of loss of kidney function is significant,” said Khurana.
In 2006, the U.S. Food and Drug Administration (FDA) put a black-box warning on the OSPS, recommending 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 US 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.
Colonoscopy is recommended for men and women over the age of 50 every 10 years to screen for polyps and other signs of colorectal cancer. Those in high-risk groups are encouraged to undergo screenings at earlier. Colonscopy involves the insertion of a slender, flexible lighted tube, fitted with a video camera, throughout the entire colon. Sigmoidoscopy uses a similar but shorter tube to examine the lower colon. Patients must avoid solid foods the day before the procedure and must also take a bowel cleansing liquid to empty the colon. The solution and tablets have been the preparations of choice because they are convenient, available without prescription, and require less clear liquid consumption than the polyethylene glycol solution.