Zerenex data heralds a tricky future for Keryx


The success of Keryx Biopharmaceuticals’ phosphate binder Zerenex in a phase III trial positions the company to submit a filing early this year, and suggests that the drug has potential to become a first-in-class therapy. The trial data also caused Keryx’s share price to skyrocket by 77% yesterday to close at $6.06. In early trading today, the stock rose a further 41%.

Keryx’s stock price is now even higher than it was before the disastrous failure of its cancer drug perifosine last April caused it to crash by almost 70% to $1.58 (Perifosine failure has Keryx pivoting away from cancer drugs, April 3, 2012). But the two biggest-selling hyperphosphataemia drugs will go generic next year. If it is to make headway in a difficult market, Zerenex will have to live up to that first-in-class promise.

Secondary endpoints

The year-long study enrolled 441 patients with end-stage kidney disease being treated with haemodialysis or peritoneal dialysis. Hyperphosphataemia is common in patients with chronic kidney disease; its symptoms include bone disorders and ossification of soft tissues in the lungs, eyes and arteries.

Zerenex (ferric citrate) convincingly met the study’s primary endpoint – reduction of blood phosphate levels when compared with placebo – with high statistical significance (p<0.0001), nicely showcasing its ability to do its job. Added to the drug’s safety profile, which is comparable to or slightly better than that of the approved drugs, this makes approval that much more likely.

When it comes to how the drug will fare when it reaches market, however, it is the secondary endpoints that hold the key. If approved this year or next, Zerenex will hit the stands at the same time as generic versions of Shire's Fosrenol and Sanofi's Renagel and Renvela, the current market leaders. Zerenex must differentiate itself if it has a hope of taking a decent share.

In the trial, Zerenex increased ferritin and transferrin saturation compared with placebo, thereby reducing the need for the intravenous iron by 52% and erythropoiesis-stimulating agents by 27%. These drugs are necessary as dialysis patients must limit iron-rich foods in their diet and suffer blood loss during the haemodialysis process.


As well as an encumbrance for patients, these additional drugs are very expensive. If Keryx can build a pharmacoeconomic case around this, payers could find Zerenex hard to resist. Analysts from Stifel Nicolaus wrote in a note that Zerenex could attain peak sales of around $250m-$300m in the dialysis setting.

And Keryx can build on that: it has started a phase II trial of Zerenex in anaemic pre-dialysis chronic kidney disease patients, geared towards expanding the drug’s eventual patient population. But first things first. Keryx plans to file for regulatory approval of Zerenex in both the US and Europe in the second quarter of 2013.

According to EvaluatePharma, Keryx has cash reserves of around $20m, which analysts from Roth Capital Partners say is enough to see it well beyond planned regulatory filings for Zerenex. That said, the company is now in a strong position to negotiate licensing deals.

If Zerenex does become the go-to phosphate binder, especially in the expanded population, a partner could make its money back may times. It would be unwise, though, to ignore the generic threat.

Study Trial ID
Phase III safety and efficacy trial in patients with
end-stage renal disease on dialysis

To contact the writer of this story email Elizabeth Cairns in London at elizabethc@epvantage.com or follow @LizEPVantage on Twitter

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