Regulators in the USA have given the thumbs-up for Keryx Biopharmaceuticals chronic kidney disease drug ferric citrate but warned about the danger of iron load.

The Food and Drug Administration has approved ferric citrate, formerly known as Zerenex, for the control of serum phosphorus levels in patients with chronic kidney disease (CKD) on dialysis. Keryx also noted that the treatment’s “pharmacodynamic properties resulted in increased ferritin and transferrin saturation, which “remained relatively constant in patients treated with active control”, i.e. with Sanofi’s market-leading phosphate binder Renvela (sevelamer carbonate) and/or now-genericised PhosLo (calcium acetate).

This increase in iron levels should enable patients to reduce use of anaemia drugs often taken by dialysis patients, the company has argued. However, the FDA label warns that ferric citrate can cause iron overload and that doctors must monitor iron parameters, the news of which sent Keryx shares down 7%.

The company quoted Julia Lewis of the Vanderbilt University Medical Center as saying that ferric citrate offers clear benefits to patients (with a low pill burden of 2-3 tablets) “and represents a new way for physicians to manage hyperphosphatemia”. She acknowledged the issue of increases in iron stores, saying that doctors “may need to reduce the dose of or discontinue IV iron therapy”.

Recently, the FDA told the company it could not use Zerenex as a brand-name for fear of confusion with another treatment but Keryx expects to have one in place before a launch, which is expected before year-end. As well as Renvela, ferric citrate will go up against Vifor Fresenius Medical Care Renal Pharma’s Velphoro (sucroferric oxyhydroxide).