Keryx' shares fall as FDA approves kidney drug, but with warnings

US drugmaker Keryx Biopharmaceuticals (Nasdaq: KERX) has received approval from the US Food and Drug Administration for ferric citrate (formerly known as Zerenex) for the control of serum phosphorus levels in patients with chronic kidney disease (CKD) on dialysis.

However, the approval came with an unexpected safety warning: ferric citrate must carry a label specifying that patients being given additional iron intravenously might need to cut dosage or stop additional iron therapy as the treatment has been shown to increase iron levels. After slumping as much as 22% in earlier trading, stock closed down 5.4% to $17.01 on Friday.

"We are thrilled with the FDA's decision to approve Ferric Citrate, and look forward to bringing it to market in the USA within the next 12 weeks," said Ron Bentsur, chief executive of Keryx, adding: "We are committed to bringing innovative therapies to the market for patients with kidney disease and are excited to be offering this important treatment option to dialysis patients."