Keryx Pharmaceuticals (NASDAQ:KERX) announced phase 3 results for chronic kidney disease drug Zerenex that made CEO Ron Bentsur say he was "thrilled." No doubt. The company's shares skyrocketed more than 40% in early trading today on the clinical study news. The results really were that good.

Examining the results
Zerenex targets treatment of hyperphosphatemia, an elevated level of phosphates in the blood that occurs in many patients with end-stage renal disease, or ESRD. The consequences of these high phosphate levels can be extremely serious, including calcification of arteries and heart problems.

The phase 3 study found that Zerenex reduced patients' mean serum phosphorus levels by 0.3 mg/DL during the four-week efficacy assessment period, while patients taking placebo saw their levels go up by 1.9 mg/DL. The statistical significance of that improvement is quite high and allowed Zerenex to easily meet the primary endpoint of the study.

That wasn't the only good news. Zerenex met several key secondary endpoints as well. The drug maintained serum phosphorus levels in the normal range over a 52-week safety assessment period. It also reduced the need for intravenous iron and erythropoiesis-stimulating agents compared to patients taking already-approved chronic kidney disease drugs Renvela from Sanofi (NASDAQ:SNY) and Fosrenol from Shire (NASDAQ: SHPG).   

From a safety standpoint, there didn't appear to be any serious causes for concern. Side effects included feces discoloration, diarrhea, vomiting, and constipation. However, these adverse events were typically classified as mild to moderate. They also occurred either in similar or lower percentages than with patients taking Renvela and Fosrenol.

Looking ahead
Keryx plans to move forward quickly with filing for regulatory approval. The company stated that it would submit a New Drug Application to the Food and Drug Administration and a Marketing Authorization Application to the European Medicines Agency in second quarter. The odds appear to be pretty good for gaining approvals. 

The overwhelmingly positive phase 3 results also seem to bode well for the prospects of another Zerenex clinical study. The drug is in a phase 2 trial for management of phosphorus and iron deficiency in anemic patients with chronic kidney disease who aren't on dialysis. 

Perhaps the biggest challenge for Keryx is in commercializing Zerenex. Renvela and Fosrenol will soon have generic versions on the market. However, the clinical study results showing Zerenex in a favorable light compared to the two brand drugs could help Keryx in gaining market share. This obstacle now might not be as difficult to overcome as it once appeared.

Primary endpoint met. Key secondary endpoints met. Stock up more than 40%. Keryx management and shareholders deserve to be thrilled.

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