updated 12/11/2008 5:09:55 PM ET 2008-12-11T22:09:55

Federal health officials said Thursday they will add the sternest safety warnings available to drugs used before colonoscopies, following reports of kidney damage in several patients.

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The Food and Drug Administration said it has received more than 20 reports of a serious form of kidney failure among patients taking the bowel-cleansing drugs, known as oral phosphate products.

The new boxed warning label will apply to Visicol and OsmoPrep — both prescription tablets made by Salix Pharmaceuticals. The label warns that the drugs should be used with caution in patients older than 55, those who suffer from dehydration and kidney disease, and those who take medications that affect the kidneys.

Regulators said they are also concerned about the risks of over-the-counter bowel cleansers, such as Fleet Phospho-soda, made by C.B. Fleet Company Inc.

“There are many people who use these and use them fine,” said Charles Ganley, who heads FDA’s office of nonprescription products. “But there are people who are developing severe kidney injury, and it’s important we try and identify who is at risk.”

FDA officials said some patients are not following directions outlined on the drugs, which instruct patients to drink up to half a gallon of water with the tablets.

“The question is one of getting people to drink enough fluids,” said Dr. Joyce Korvick, director of FDA’s digestive products. “Some patients that take these pills feel perhaps you don’t need to drink as much as you really do to avoid these side effects.”

Korvick said kidney damage can occur within days or weeks of using the drugs, but symptoms — such as lethargy, drowsiness and swelling — may not appear until much later.

‘Patient tolerability’
FDA is requiring Salix to distribute a medication guide warning patients about the risks of the drugs. The company also must conduct a follow-up study looking at which patients are most vulnerable to kidney damage.

Salix’s tablets compete against a number of liquid bowel cleansers, known as polyethylene glycol solutions. Products in that family include Braintree Laboratories’ GoLytely and Schwarz Pharma’s Colyte.

Regulators stopped short of recommending those medications as safer options, noting that they also require patients to flush their systems with large amounts of water.

“It’s basically a question of patient tolerability,” Korvick said. “To take the polyethylene glycolated products you need to drink two to three gallons of water, depending on what product you choose. So the patient may not be able to comply with that.”

FDA officials also highlighted the risks of over-the-counter bowel cleansers, though all the problems reported to the agency were connected with prescription products. FDA said many over-the-counter phosphate products are labeled only to treat constipation, but patients use them at higher doses to clear the colon.

“When used for bowel cleansing, these products have the same risks as prescription” drugs, the FDA said in a statement.

The agency advised consumers not to use any of the over-the-counter products for bowel cleansing. While nonprescription products cannot receive boxed warnings, FDA officials said they hope to update labeling on the dozens of over-the-counter phosphate drugs by next spring.

The FDA first warned doctors and patients about potential kidney risks with the medications in 2006. A petition submitted to the agency last September called on regulators to place a boxed warning on the drugs.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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