Some drugs prescribed to dialysis patients contain high levels of phosphorus, according to a paper published in Kidney International. Dialysis patients must limit phosphorous because dialysis removes only a small amount of phosphorus from the blood. 

While the presence of phosphorus in medications is listed on their labels, the amounts were essentially unknown until a research team at Rutgers Robert Wood Johnson Medical School led by Richard Sherman, a professor of medicine in the department of medicine, decided to take a closer look.

“I knew from looking at the ingredients that there was phosphorus, I just didn’t think it would be clinically significant,” Sherman said. “The amounts we found were a surprise.”

The Rutgers researchers explain that 23 of the 200 most-prescribed medications they surveyed in a national chain of dialysis centers listed phosphorus-containing ingredients, but not their amounts. Through their research, Sherman’s team discovered a number of the drugs contained high levels of phosphorus.

“These drugs are ‘cures’ given by physicians,” the study concludes. “As their phosphorus content may well be injurious, there is a moral imperative that action be taken to ameliorate it.”

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While the phosphorous burden imposed by the medications is probably minor for most patients, the authors concluded, “a close examination of the issue suggests that the burden may be notable in some.”

High blood levels of phosphorus resulting from kidney failure can weaken bones, cause heart problems, build up calcium deposits in the arteries, joints, skin or lungs, and lead to other health problems.

When drug makers were unable to provide the amounts of phosphorus in their medications, the Rutgers team performed their own analyses. The amount of phosphorus exceeded 30 mg per tablet in some manufacturer’s forms of such commonly prescribed drugs as amlodipine and lisinopril; one formulation of paroxetine had 111.5 mg per dose.

The levels of phosphorus did not necessarily increase with the size of the dose, and brand versus generic forms of medications did not prove to be a factor. 

Sherman said he was awarded a grant by Dialysis Clinic Inc. of Nashville, Tennessee, to fund his research, which began as a “shot in the dark.”  He said he did not believe drug makers were withholding information from his team, but rather that the manufacturers were unaware of the levels of phosphorous in their medications and its potential clinical importance to patients with kidney disease.

The issue is further complicated by the number of medications involved, their varying dosages and forms, the potential for changes in inert ingredients over time and the wide array of generic manufacturers. The level of phosphorus in a specific drug could vary simply by the region in which it is manufactured, Sherman noted.

Given those factors, Sherman said the most practical solution would be raising awareness among physicians who treat dialysis patients and identifying those medications that may not be “dialysis safe” because of high phosphorus content. 

Sherman has created a petition that requests the Commissioner of Food and Drugs at the U.S. Food and Drug Administration require that drug manufacturers report the phosphorus content of their products and, when equal to 10 mg or more, note this in the Warning/Precaution and Special Population sections of the product's package insert. The petition can be viewed, and signed, here.

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