FDA warning dampens Keryx's parade for newly approved kidney drug

While Keryx ($KERX) was waiting for the FDA to come through on a marketing decision for ferric citrate (formerly Zerenex), a new treatment to deal with complications of kidney disease, the biotech made much of the drug's ability to help its target group avoid anemia drugs by boosting their iron levels. But when the FDA came through with their expected approval on Friday, a label warning that the drug could wind up triggering iron overload dampened analysts' enthusiasm for this treatment considerably. And Keryx's stock price reflected the damage, ending Friday down 5%.

The drug was approved for cases of hyperphosphatemia, or elevated levels of phosphates. The condition afflicts some 375,000 patients on dialysis, representing a hefty market Keryx believes is potentially worth more than $1 billion. But some analysts fretted that the label could hold Keryx back from realizing the drug's full potential.

"The expectations were that the label would have an indication for anemia management," FBR Capital Markets analyst Andrew Berens told the Associated Press. "Instead where it appeared was in the warning section, which is kind of strange because it's like turning a benefit into a warning."

It wasn't supposed to work that way. Keryx had touted the drug's secondary benefits as a way to stand out from the crowd of phosphate-lowering drugs. Sanofi's Renvela and Shire's Fosrenol are nearing the patent cliff, with cheaper generics set to flood the market and complicate the arrival of ferric citrate. Keryx also has to come up with a new name to market the drug, after the FDA rescinded approval for Zerenex.

But the biotech is committed to make do with what it has.

Dr. Julia Lewis

"I believe that ferric citrate offers clear benefits to patients and represents a new way for physicians to manage hyperphosphatemia," said lead investigator Dr. Julia Lewis, a nephrologist and professor of Medicine at Vanderbilt University Medical Center. "Given ferric citrate's pharmacodynamic properties that lead to increases in iron stores, physicians should assess and monitor iron parameters and may need to reduce the dose of or discontinue IV iron therapy."

- here's the release
- and here's the AP story

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