Chronic Kidney Failure Linked to Certain Bowel Cleansing Products Used Prior to Colonoscopy

Researchers from the Columbia College of Physicians & Surgeons in New York reporting in the November 2005 Journal of the American Society of Nephrology identified those bowel cleansing drugs containing sodium phosphate as an under-recognized cause of chronic kidney failure. These bowel cleansing products are frequently used prior to colonoscopy. Colonoscopy is an important medical procedure that is used to screen for bowel cancer and should be performed more frequently, especially in people over the age of 50, using products that do not cause this problem.    

The Columbia researchers reviewed all kidney biopsies that were received in their facility between January 2000 and December 2004 for the presence of kidney damage due to phosphate toxicity. A biopsy is a diagnostic procedure that involves the removal of tissue — kidney tissue, in this study — from patients with certain types of medical problems and examining them under a microscope. A total of 7,349 kidney biopsies were reviewed.    

From the biopsies, the researchers identified 31 patients who had kidney damage that was consistent with phosphate toxicity. One of the things the researchers wanted to know was how many of these patients had used a phosphate-containing bowel cleansing product prior to their kidney problems. To determine this number, the medical records for the patients were reviewed for the use of a bowel-cleansing agent prior to colonoscopy, as well as age, gender, ethnicity, medical history, drug history, and kidney function before and after the colonoscopy.

Common sodium phosphate-containing bowel cleansing drugs include the non-prescription product Fleet Phospho-soda and Visicol, a prescription-only oral tablet. The Fleet product and its generic equivalents will have its active ingredients — monobasic sodium phosphate monohydrate and dibasic sodium phosphate heptahydrate — on their labels. Visicol contains essentially the same active ingredients.

Of the 31 patients who had kidney damage that was consistent with phosphate toxicity, two patients were excluded because there was no history of colonoscopy. Two others patients were excluded because they had unexplained reasons for their phosphate toxicity. An additional two patients were not included in the study’s final analysis because neither the physician nor the patient could remember what type of bowel cleansing preparation was used. Four patients who had undergone kidney transplantation were also excluded.

This left 21 patients with kidney damage from phosphate. With the exception of one patient, all took oral phosphate solutions such as Fleet Phospho-soda. Of these 21 patients, 17 were women and four men, with an average age of 62 years.  A majority of these 21 patients (16, or 76.2 percent) had a history of high blood pressure. Of the 16 patients with high blood pressure, 14 (87.5 percent) were treated with either an angiotensin converting enzyme (ACE) inhibitor or an angiotensin receptor blocker (ARB). The ACE inhibitor family includes such popular drugs as lisinopril (ZESTRIL) and ARB agents includes drugs such as losartan (COZAAR).  

Patients presented for medical care with acute kidney problems at a median of one month after their colonoscopies. In a few of these patients, kidney problems were discovered within three days of their colonoscopy, at which time hyperphosphatemia (abnormally high levels of phosphates in the blood) was documented.

Four of the 21 patients required permanent dialysis (filtering of the blood). One of these four had then received a successful kidney transplant. Among the remaining 17 patients, 16 patients showed improvement in their kidney function. Though kidney function may improve, all 21 patients included in this study were left with chronic kidney failure.

The Columbia researchers cited several potential factors that may contribute to development of kidney problems from sodium phosphate-containing bowel cleansing agents. These are inadequate hydration (not enough water); older age; history of high blood pressure and arteriosclerosis (clogging of blood vessels); and the use of ACE inhibitors, ARB blockers, water pills (diuretics), or nonsteroidal anti-inflammatory drugs (NSAIDs) such as celecoxib (CELEBREX) or ibuprofen (MOTRIN).    

One issue not addressed by the Columbia study is the use of Fleet Phospho-soda and similar products for constipation rather than only for bowel cleansing prior to colonoscopy. There are consumers who chronically, and sometimes inappropriately, use laxatives such as Fleet Phospho-soda for long-term constipation. The extent to which the chronic use of Fleet Phospho-soda or similar products may contribute to chronic kidney problems is unknown. However, it should be considered by consumers before they use sodium phosphate products and by physicians who encounter patients with acute kidney problems.

What You Can Do

You should talk to your physician prior to a colonoscopy or other procedure that requires a sodium phosphate bowel cleansing drug about the possibility of phosphate-induced kidney toxicity. There are alternative methods of pre-colonoscopy bowel cleansing that are effective but do not involve the use of sodium phosphate. Two of the most commonly used products are Colyte and TriLyte, which are oral solutions available by prescription. As mentioned above, colonoscopy can be a life-saving screening tool because it can discover early evidence of colon cancer before it is too late for a cure.

You should consult a physician if you chronically use a sodium phosphate-containing drug for constipation regarding the possibility of kidney toxicity.

If you experience an adverse effect from any FDA regulated product, including sodium phosphate-containing products, it should be reported to the agency.