Keryx Biopharmaceuticals has completed patient enrollment in the long-term study component of its phase III registration program of Zerenex, the company's ferric iron-based phosphate binder for the treatment of elevated serum phosphorus levels, or hyperphosphatemia, in patients with end-stage renal disease (ESRD) on dialysis. The Zerenex phase III registration program, which is being conducted pursuant to a Special Protocol Assessment (SPA) with the FDA, is comprised of an already successfully-completed phase III short-term study, and this ongoing phase III long-term study.

This phase III long-term study is a multicenter, randomized, open-label, safety and efficacy clinical trial in over 400 ESRD patients on hemodialysis or peritoneal dialysis. The study consists of a 2-week washout period followed by a 52-week safety assessment in which patients are randomized 2:1 to receive either Zerenex or an active control. The 52-week safety assessment period is followed by a 4-week efficacy assessment.  During the 4-week efficacy assessment, only those patients randomized to treatment with Zerenex during the safety assessment period will be randomized in a 1:1 ratio to either continue treatment with Zerenex or to be switched to placebo for a 4-week period.