Shares in Keryx Biopharmaceuticals have shot up after the firm presented positive late-stage data for its kidney disease treatment Zerenex.

Top-line results from the long-term Phase III study of Zerenex (ferric citrate), the company's phosphate binder for the treatment of elevated serum phosphorus levels, or hyperphosphatemia, in patients with end-stage renal disease on dialysis. The drug met the study's primary endpoint, demonstrating a highly statistically significant change in serum phosphorus versus placebo.

In addition, Zerenex met the key secondary endpoints of increasing ferritin and transferrin saturation and reducing the use of intravenous iron and erythropoiesis-stimulating agents, such as Amgen’s Aranesp (darbepoetin alfa) and Epogen (epoetin alfa). Keryx says it now expects to submit the drug in the USA and Europe in the second quarter of 2013.

Julia Lewis of the Vanderbilt University School of Medicine in Nashville, and head of the Phase III programme, said "there is a clear need for viable alternatives to the marketed phosphate binders, and Zerenex can play a major role by not only providing adequate phosphate binding, but also providing additional benefits".

The market is currently dominated by Sanofi's sevelamer-based kidney disease treatments Renagel and Renvela, and  other available phosphate binders include Shire's (lanthanum carbonate) and Fresenius Medical Care's PhosLo (calcium acetate). Vifor Pharma's PA21 (iron(III)-oxyhydroxide) for treating hyperphosphatemia has been submitted for approval in the European Union and a filing is imminent in the USA.

The promising data has gone down well with investors and Keryx stock leapt 77% to $6.06. The company's partner Japan Tobacco filed Zerenex with the Japanese Ministry of Health, Labour and Welfare for marketing approval earlier this month.