COLONOSCOPY PREPARATION DANGERS. What I Tell Patients

In order to perform an adequate colonoscopy the physician wants to make sure that the colon is cleansed of all fecal matter. This makes it easier to visualize the entire colon so as to minimize the dangers of missing a hidden cancer or polyp. For that reason the physician prescribes a pre colonoscopy cleansing program or a “colon prep.”

As most people know, from a live colonoscopic viewing of TV newscaster Katie Couric, colonoscopy is the recommended test for early detection of colon cancer and the lesions that precede it. After the introduction of full Medicare coverage in the US, the rate of screening colonoscopy increased from 285 procedures per 100,000 people each quarter in 1997 to 1,919 procedures per 100,000 people each quarter in 2002. Polyethylene glycol solution (PEGS) and oral sodium phosphate solution (OSPS) are the agents most commonly used to prepare the patient for colonoscopy. A higher volume of liquid needs to be ingested if PEGS rather than OSPS is to be used, which had led to the widespread use of OSPS.

Since 2004, however, reports have linked use of OSPS to deterioration of renal function in some patients. The current belief is that OSPS causes transient hyperphosphatemia, which, in combination with volume depletion, causes calcium phosphate crystals to be deposited in renal tubules. Within a few hours to 21 days after a colonoscopy or colon surgery where Fleet Phospho-soda or another oral sodium phosphate product was used for bowel prep, symptoms may develop like fluid retention, high blood pressure, irregular heartbeat, muscle twitching and seizures. The FDA has confirmed that at least 21 people developed acute phosphate nephropathy after using oral sodium phosphate solutions like Fleet Phospho-soda.

In December 2008, the FDA* issued a boxed warning, to be placed in the package insert of OSPS products, that advises of the potential risk of kidney damage associated with their use.

Fleet Phospho-soda [C.B. Fleet Company, Inc.] was the oral sodium phosphate solution commonly used to relieve constipation or as a bowel cleanser prior to a colonoscopy. Fleet Phospho-soda started as an over-the-counter product which was safely used for a number of years as a laxative. However, during the 1990s, the manufacturer began marketing the product for use at double doses to cleanse the bowels as part of a colonoscopy prep. When it is used at higher doses for colonoscopy prep, however, it can cause a form of kidney damage. Double doses of Fleet Phospho-soda are not approved by the FDA nor determined to be safe, because it could lead to:

• Acute Phosphate Nephropathy
• Kidney Damage or Renal Disease
• Dialysis
• Kidney Transplant
• Death

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*In December 2008, the FDA indicated that Fleet Phospho-soda should not be used over-the-counter as a bowel prep. In response, a recall was issued and the following products are no longer on the over-the-counter a market:
• Fleet Phospho Soda Oral Saline Laxative
• Fleet Phospho-Soda EZ-Prep Bowel Cleansing System
• Fleet Phospho Accu-Prep
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The risk of acute phosphate nephropathy is greater among
• those who are over 55 years old,
• those who suffer from dehydration,
• kidney disease,
• acute colitis or
• delayed bowel emptying, and
• those who are taking medications that affect the kidney, like fluid pills, blood pressure, heart failure or kidney failure drugs.

I believe that PEGS is a safer option than OSPS, and an effective alternative to it.
Many other gastroenterologists think the same way, because the use of OSPS for colonoscopy has declined from 88% of procedures in 2004 to 48.4% in 2006.
Increased awareness has also led to discontinuation of over-the-counter OSPS products, and will probably decrease the incidence of postcolonoscopy kidney injury.

*[Food & Drug Administration. Oral sodium phosphate (OSP) products for bowel cleansing (marketed as Visicol and OsmoPrep, and oral sodium phosphate products available without a prescription) http://www.fda.gov/cder/drug/infopage/OSP_solution/default.html (2009).
The effect of oral sodium phosphate drug products on renal function in adults undergoing bowel endoscopy.]