Oral Sodium Phosphate Products Linked to Acute Phosphate Nephropathy

Laurie Barclay, MD

Disclosures

December 12, 2008

December 12, 2008 — Acute phosphate nephropathy has been reported in association with the use of oral sodium phosphate products (OSPs), the US Food and Drug Administration (FDA) announced yesterday.

The FDA has therefore required the manufacturer of prescription OSPs Visicol (Salix Pharmaceuticals) and OsmoPrep (Salix Pharmaceuticals) to add a boxed warning to the labeling for these products, according to an alert sent yesterday from MedWatch, the FDA's safety information and adverse event reporting program.

"Though rare, these are serious adverse events associated with the use of oral sodium phosphates — both prescription and over-the-counter products," Janet Woodcock, MD, director of FDA's Center for Drug Evaluation and Research, said in a news release.

"In some cases, these serious adverse events occurred in patients with no pre-existing health factors that would have put them at risk for developing kidney injury," Dr. Woodcock said. "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."

In addition to Visicol and OsmoPrep, which are used for bowel cleansing and preparation before colonoscopy or other procedures, OSPs include over-the-counter laxatives such as Fleet Phospho-soda (C. B. Fleet Company).

When used for bowel cleansing, OSPs have been linked to acute phosphate nephropathy in some patients without apparent risk factors for developing acute kidney injury. However, some of these patients may have been dehydrated before using OSPs or may have had inadequate fluid intake after use of OSPs, which would increase the risk for acute phosphate nephropathy.

In acute phosphate nephropathy, calcium-phosphate crystals deposit in the renal tubules, where they may cause serious, permanent impairment of kidney function.

Risk factors for developing acute phosphate nephropathy as an adverse event of OSP use include age greater than 55 years, hypovolemia, decreased intravascular volume, and renal impairment, bowel obstruction, or active colitis at baseline. Use of medications that may impair renal perfusion or function may also increase risk. These include diuretics, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, and possibly nonsteroidal anti-inflammatory drugs.

For patients with any of the above risk factors, the FDA recommends that OSP prescription products be used with caution for bowel cleansing. OSP products are contraindicated in children younger than 18 years or in combination with other laxatives containing sodium phosphate.

To ensure that the benefits of OSPs outweigh the risks of acute phosphate nephropathy, the FDA is mandating a risk evaluation and mitigation strategy by the manufacturer, including a medication guide, as well as a postmarketing clinical trial to further evaluate the risk of acute renal injury with OSP use.

Because OSPs have a long history of safe use as over-the-counter laxatives, the FDA will continue to allow their availability in this setting. However, the FDA warns that over-the-counter laxative OSPs should not be used for bowel cleansing at a higher dose than the recommended laxative dose, and it will issue an amendment to remove the professional labeling for bowel cleansing for these OSPs available over-the-counter. OSPs should only be used for bowel cleansing when prescribed by a healthcare professional.

Adverse events related to use of OSPs should be communicated to the FDA's MedWatch reporting program by telephone at 1-800-FDA-1088, by fax at 1-800-FDA-0178, online at http://www.fda.gov/medwatch, or by mail to 5600 Fishers Lane, Rockville, MD 20852-9787.

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