Oral phosphate sodium drugs, including the over-the-counter drug Fleet Phospho-soda (manufactured by C.B. Fleet Inc.), and the prescription drugs Visicol and OsmoPrep (both manufactured by Salix Pharmaceuticals), are laxatives and bowel-cleansers, often used by doctors before colonoscopies and similar procedures. In late 2008, the FDA added a black box warning (the most stringent warning available) to these products.
The danger of the drugs is that they may cause acute phosphate nephropathy, a serious kidney injury which is characterized by the accumulation of calcium-phosphate crystals in renal tubles, renal impairment, and sometimes death. Affected patients may require dialysis or kidney transplants. Symptoms include lethargy, low urine output, and swollen legs and ankles. Patients are at a higher risk of contracting acute phosphate nephropathy if they are: over 55, dehydrated, have a history of kidney problems, have active bowel colitis, or take other medications that affect kidney function.
C.B. Fleet did an admirable job of voluntarily recalling its products once the FDA notice came along. They will work with the FDA to determine if their products are better used by prescription, only. However, they may have had an obligation to take action even sooner—the overworked folks at the FDA cannot be responsible for setting the benchmarks for response to injuries and complaints. Tellingly, there have been indications of problems since 2003, when a medical case report was published about acute phosphate nephropathy and renal insufficiency in a woman who took OsmoPrep. Then, in 2005, doctors published an article describing injuries, including renal failure, to 21 people who used OsmoPrep products. More potential cases were later identified by the FDA’s Adverse Event Reporting System.
You can see the FDA’s April, 2009 notice about the stronger boxed warnings here.