What: Shares of Keryx Biopharmaceuticals (NASDAQ:KERX), a drug developer with a focus on renal disease, fell more than 15% today on heavy volume.

So what: Keryx actually released some good news today as the company announced that the Committee for Medicinal Products for Human Use, or CHMP, of the European Medicine Agency adopted a positive opinion for Keryx's drug Fexeric.

Fexeric, which helps patients with chronic kidney disease on dialysis control their phosphorus levels, should hear an official decision on approval within two to three months, as that is the typical time period after CHMP releases their opinion. Fexeric already has FDA approval in the U.S. and sells under the brand name Auryxia, so today's release is certainly a positive sign for Keryx investors. 

So if the news was good, why did the stock fall?

Today's movement is probably because of Roth Capital, which recently affirmed its buy rating on Keryx stock, but dropped the price target all the way to $11 from $23. The report was generally upbeat on the positive news from CHMP, but noted that manufacturing capacity issues are likely to act as a near term barrier for the company before it can expand into Europe.

In addition, disappointing initial sales for Auryxia in the U.S. have increased the firm's trepidation on the drug, noting that prescriptions have taken a dip recently. They ended by saying "We believe Keryx will remain highly volatile and recommend owning shares by only the most risk tolerant investors currently." 

Now what: While it certainly looks like Auryxia prescriptions have taken a small dip recently, it is hard to interpret much of a trend based on the available prescription data.

Source: Bloomberg Intelligence

Still, while Auryxia could hold a lot of promise, sales have been slower out of the gate than many investors were hoping for, and the stock has slumped on the results. I think it's wise for investors to continue to watch Auryxia sales from the sidelines, and wait until we get a clear signal that sales are gaining traction. Until that happens I have a hard time seeing Keryx stock a compelling opportunity, even considering today's lower price.