Warnings Sounded About Oral Sodium Phosphates

Tacoma, WAPatients who used an oral sodium phosphate (OSP) such as Visicol, OsmoPrep or Fleet Phospho-soda prior to a colonoscopy may be at an increased risk of kidney damage. A box warning from the FDA notes that when such products are used to prepare bowels for a colonoscopy patients face a risk of acute phosphate nephropathy. The same risk does not appear to apply when the OSPs are used as a laxative.

Some patients are at a greater risk of developing kidney nephropathy than others. Those include patients who are taking ACE inhibitors, angiotensin receptor blockers (ARBs) or NSAIDs when they use the OSP, are 55 years or older or are dehydrated or have a bowel obstruction or colitis when they use the OSP.

A study published in the journal Nature Clinical Practice Nephrology (September 26, 2008), found that the use of OSPs as a bowel preparation before colonoscopy was linked to a risk of acute phosphate nephropathy. Furthermore, they found, "OSP is associated with clinically relevant electrolyte abnormalities, including hypokalemia, hyperphosphatemia, and hypocalcemia, particularly in elderly patients."

The researcher concluded that the use of OSPs in older patients or in those who already have risk factors for acute phosphate nephropathy should be avoided until safer preparations are available. If they cannot be avoided, the researchers recommend that patients be given adequate fluid and delay, reduce or replace the second dose of OSP to decrease the risk of renal damage.

This study was not the first to sound the alarm about OSPs. In 2006, a joint task force of the American Society of Colon and Rectal Surgeons, the American Society for Gastrointestinal Endoscopy and the Society of American Gastrointestinal and Endoscopic Surgeons issued a consensus statement about bowel preparations. The statement noted that bowel preparations should be selected based on a safety profile of the agent and with consideration to the patient's overall health. Specifically, some patients might be advised to use different solutions as a bowel preparation.

OsmoPrep and Visicol are prescription medications. They now carry a black box warning alerting patients to the potential of renal failure when used at high doses. The FDA has also recommended that Fleet Phospho-soda, an over-the-counter laxative, should only be available by prescription when it is used as a bowel cleanser. The product's maker, C.B. Fleet Co., announced a voluntary recall of the product after the FDA's announcement.