Oral Sodium Phosphate Products: Prescription Only

Lynchburg, VAIn response to renal risks of oral sodium phosphate products, on February 9, 2009 the FDA recommended that only prescription oral sodium phosphate (OSP) bowel preparations be used by patients for bowel cleansing prior to undergoing colonoscopy (colon examination). Patients routinely take OSP products to cleanse the bowel before a colonoscopy and other medical procedures.

The agency also is requiring "black box" warnings for two prescription products made by Salix Pharmaceuticals--Visicol and OsmoPrep. Over-the-counter bowel preps, namely Fleet Phospho-soda and Fleet Phospho-soda EZ-Prep were voluntarily recalled by C.B. Fleet in December, 2008.

How safe are prescription OSP products?

"The problem with current sodium phosphate-based preparations is that the phosphate load is too much for the kidney to handle," said nephrologist Howard Lien, MD, PhD, whose article was published in Nature Clinical Practice-Nephrology (2008;4:606-614). "Since phosphate can cause multiple renal and electrolyte problems, such as low serum levels of potassium and calcium, I would recommend using polyethylene glycol-based bowel-cleansing products while waiting for a better preparation."

While these over-the-counter products do not show a risk of kidney injury when used as a laxative, they have the same risks as prescription OSPs when used as a bowel cleanser, also known as a "purgative". Therefore, the FDA has warned consumers not to use over-the-counter OSPs for bowel cleansing.

The FDA has received reports of serious adverse events occurring in patients taking OSPs with no pre-existing health factors that would have put them at risk for developing kidney injury. "We cannot rule out, however, that some of these patients were dehydrated prior to ingestion of OSP products or they did not drink sufficient fluids after ingesting OSP products," said Janet Woodcock, M.D., director, FDA's Center for Drug Evaluation and Research. Since 2006, the agency received reports of 20 cases of kidney injury associated with the use of OsmoPrep.

OSP products should not be used by children under 18 years of age or in combination with other laxative products containing sodium phosphate. The FDA is recommending that OSP prescription products be used with caution for bowel cleansing by the following at risk groups:
* People over 55 years of age,
* People who suffer from dehydration, kidney disease, acute colitis, or delayed bowel emptying, and
* People taking certain medicines that affect kidney function, such as diuretics (fluid pills), angiotensin converting enzyme inhibitors (medications that lower blood pressure) angiotensin receptor blockers, (used to treat high blood pressure, heart or kidney failure) and possibly nonsteroidal anti-inflammatory drugs (similar to ibuprofen and other arthritis medications).


OSP Future

Currently, boxed warnings are not used for over-the-counter (OTC) products, " but the agency plans to issue an amended label for OTC OSP products by May of 2009," said Dr. Charles Ganley, director of the FDA's Office of Nonprescription Products.

The FDA has asked Salix to develop a risk evaluation and mitigation strategy--known as REMS--for its products Visicol and OsmoPrep and to assess the risk of acute phosphate nephropathy (acute kidney injury). Salix Pharmaceuticals, Ltd., headquartered in Raleigh, North Carolina, develops and markets prescription pharmaceutical products for the treatment of gastrointestinal diseases. The drug company also has to distribute a Medication Guide to alert patients to the risk of acute kidney injury associated with the use of these products, and to conduct a postmarketing clinical trial to further assess the risk of acute kidney injury with the use of its products.

In 2005 Salix decided to "accelerate the development and filing of its next generation MCC-free purgative tablet product, INKP-102".

"The bowel cleansing market represents a dynamic and growing opportunity for Salix," said Carolyn Logan, President and Chief Executive Officer. "…We intend to capitalize on the current dynamics within the bowel cleansing market to significantly expand our business in this growing market. We are pleased to announce that effective July 1, 2009 both MOVIPREP and OSMOPREP will be added to the CVS Caremark formulary… CVS Caremark is one of the largest prescription benefit management (PBM) organizations in the U.S."