Update: Oral Sodium Phosphate Used as Preparation for Colonoscopy Can Cause Kidney Damage

The Food and Drug Administration (FDA) announced on Dec. 11, 2008, that it is requiring the manufacturer of the prescription oral sodium phosphate (OSP) products Visicol and Osmo-Prep to add a boxed warning to these products, which are often used to prepare patients for colonoscopies.

In recent months, FDA has received additional reports of acute phosphate nephropathy, a type of serious, acute kidney damage, associated with the use of OSP products for bowel cleansing prior to colonoscopy or other procedures.

Other OSP products discussed in the FDA’s announcement include those available over-the-counter without a prescription, such as laxatives (Fleet Phospho-soda).

Acute phosphate nephropathy is rare, but serious. It is associated with deposits of calcium-phosphate crystals in the renal (kidney) tubules; it may result in permanent kidney function impairment.

There are safer alternative methods to OSPs for 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.

The FDA is requiring the manufacturer of Visicol and OsmoPrep to conduct a postmarketing clinical trial to further assess the risk of acute kidney injury with use of these products.

The manufacturer also must develop and implement a risk evaluation and mitigation strategy (REMS), which will include a Medication Guide, to inform patients about benefits and risks of these products.

In its announcement, the FDA stated that, "OSP products, in addition to use for bowel preparation, have a long history of safe use as non-prescription products as laxatives (i.e. for relief of constipation) and accordingly, they will continue to be available over-the-counter for this use. But in our Worst Pills publications, Public Citizen has never recommended that these OSP products be used as laxatives. In light of the risk of acute phosphate nephropathy, over-the-counter laxative OSP products should also not be used for bowel cleansing.

Worst Pills, Best Pills News first warned our readers about acute phosphate nephropathy with bowel cleansers in March 2006. The occurrence of these events was later described in an Information for Healthcare Professionals sheet and an FDA Science Paper issued in May 2006. Additional cases of acute phosphate nephropathy have been reported to FDA and described in medical literature since these were issued.

Who Is At Risk?

Individuals who appear to have an increased risk of acute phosphate nephropathy following the use of OSPs include people:

• who are over age 55;
• who are hypovolemic or have decreased intravascular volume;
• who have baseline kidney disease, bowel obstruction, or active colitis;
• and who are using medications that affect renal perfusion or function (such as diuretics, angiotensin converting enzyme [ACE] inhibitors, angiotensin receptor blockers [ARBs], and possibly nonsteroidal anti-inflammatory drugs [NSAIDs]).

In some cases when used for bowel cleansing, acute phosphate nephropathy has occurred in patients without identifiable factors that would put them at risk for developing acute kidney injury. The FDA cannot rule out, however, that some of these patients were dehydrated prior to ingestion of OSPs or they did not drink sufficient fluids after ingesting OSP.

What You Can Do

Talk to your physician prior to a colonoscopy or other procedure that requires bowel-cleansing drugs about the possibility of phosphate-induced kidney toxicity. Also consider requesting the safer alternative methods to OSPs for pre-colonoscopy bowel cleansing mentioned above, which include the oral solutions Colyte and TriLyte, available by prescription.