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Kidney Drug Ferric Citrate Approved With Warning

Treatment controls serum phosphorus levels

The FDA has approved ferric citrate (Keryx Biopharmaceuticals), formerly known as Zerenex, for the control of serum phosphorus levels in patients with chronic kidney disease (CKD) on dialysis.

The approval was based on data from phase III trials, in which ferric citrate effectively reduced serum phosphorus levels to within the Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines range of 3.5 mg/dL to 5.5 mg/dL.

In addition to the effects on serum phosphorus levels, the pharmacodynamic properties of ferric citrate resulted in increased ferritin and transferrin saturation (TSAT), whereas these parameters remained relatively constant in patients treated with an active control (sevelamer carbonate [Renvela, Sanofi] and/or calcium acetate [PhosLo, Fresenius Medical Care]). The most common adverse events associated with ferric citrate were gastrointestinal-related and included diarrhea, nausea, vomiting, and constipation.

Recently, Keryx Biopharmaceuticals was informed by the FDA that approval of the brand name Zerenex had been rescinded. The company believes that it will have an approved brand name on or prior to launch, although a brand name is not a prerequisite for the launch of an FDA-approved drug.

In the U.S., more than 400,000 patients with end-stage renal disease (ESRD) require dialysis, and that number is projected to increase in the future. Managing ESRD is complex as many metabolic factors, such as iron and phosphorus, are out of balance. Phosphate retention and the resulting hyperphosphatemia in dialysis patients are typically associated with an increased risk of heart disease, bone disease, and death.

Most ESRD patients require chronic treatment with phosphate-binding agents to lower and maintain serum phosphorus at acceptable levels. In addition, iron can be severely depleted in dialyzed patients, who are often treated with intravenous (IV) iron and/or anemia medications, such as erythropoiesis-stimulating agents, to help boost the production of red blood cells.

Ferric citrate was approved by the FDA on September 5 and is indicated for the control of serum phosphorus levels in patients with CKD on dialysis. Keryx plans to make ferric citrate available to U.S. dialysis patients within approximately 3 months.

Ferric citrate is also being developed in the U.S. as a treatment for iron deficiency anemia in patients with stage-3 to stage-5 non–dialysis–dependent CKD. A pivotal phase III study in this indication is expected to begin in the coming weeks.

The labeling for ferric citrate includes a warning regarding the potential for iron overload. Physicians should monitor ferritin and TSAT, and should assess the need to reduce the dose of or discontinue IV iron therapy.

Sources: Keryx Biopharmaceuticals; September 5, 2014; and Ferric Citrate Prescribing Information; September 2014.

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