Oral Sodium Phosphates: Laxative vs Purgative

Washington, DCOn March 5, 2009 Health Canada issued a warning not to use oral sodium phosphates as bowel cleansers (also referred to as a "purgative") as they may cause serious adverse effects. However, the US Food and Drug Administration (FDA) recently approved safety labeling revisions to advise clinicians of the risk for acute kidney injury in patients receiving oral sodium phosphate (OSP) products.

"Just 10 days after the Health Canada warning, the FDA called for a black box warning for sodium phosphate monobasic monohydrate and sodium phosphate dibasic anhydrous tablets (Visicol and OsmoPrep; Salix Pharmaceuticals, Inc). The reason: rare, but serious, reports of "acute phosphate nephropathy" in patients who received OSP products.

Currently, OSP products are available over-the-counter and sold as natural health products in Canada. According to Health Canada, they are relatively safe to use as a laxative, but when taken for bowel cleansing (a purgative dose) they have been associated with serious side effects, including electrolyte disturbances as well as kidney injury.

Health Canada warns that the instructions for purgative use on the labels of these three products should no longer be followed, unless recommended by a health care practitioner:

1. Phoslax by Odan Laboratories Ltd.;

2. Fleet Phospho-Soda Oral Laxative by Johnson & Johnson Merck Consumer Pharmaceuticals--the manufacturer voluntarily discontinued sales in Canada;

3. Phosphate Solution by Pharmascience Inc., which is also sold under the following brand names: Option + Phosphates Solution, Pharmasave Phosphates Solution and Reserve Phosphates Solution.

Although the FDA acknowledges potential risk factors for injury associated with OSP products, particularly with increased age, its warnings aren't as severe as those of Health Canada. The FDA states the following:

"To reduce the potential for acute kidney injury, doses of sodium phosphate should be taken according to the recommended schedule (AM/PM) with adequate fluid intake before, during, and after use...Patients should not repeat a course of sodium phosphate within 7 days of original dosing. No additional enema or laxative is required, and patients should be advised not to take additional agents, particularly those containing sodium phosphate."

The FDA also says that Sodium phosphate monobasic monohydrate plus sodium phosphate dibasic anhydrous tablets are indicated for cleansing of the colon as a preparation for colonoscopy in adults 18 years and older.

Coincidentally, 4 lawsuits were filed on March 25, 2009 (the same day that the FDA issued the black box warning) against C.B. Fleet Co.'s Fleet Phospho-Soda, alleging that they promoted their over-the-counter laxative at double doses for use during colonoscopy prep, which caused the plaintiffs to develop severe and potentially life-threatening kidney failure. The lawsuits each seek more than $10 million damages as a result of kidney problems caused by the colonoscopy prep.