A 4-Week Dose-Ranging and Efficacy Trial of KRX-0502 (Ferric Citrate) in Patients With End-Stage Renal Disease

Inclusion Criteria: * Males or non-pregnant, non-lactating females * Age \> 18 years * On thrice weekly hemodialysis or peritoneal dialysis for at least the previous three months prior to Screening Visit (Visit 0) * Serum phosphorus levels ≥ 3.5 mg/dL and \< 8.0 mg/dL at Screening Visit (Visit 0) * Serum phosphorus levels \> 6.0 mg/dL during the washout period (Visits 2 or 3) * Taking 3 to 15 tablets/capsules per day of 667mg calcium acetate or 800 mg sevelamer (hydrochloride or carbonate), or any combination of these agents as reported by the patient at Screening Visit (Visit 0) * Serum ferritin \<1000micrograms/L and Transferrin Saturation (TSAT) \<50% at the Screening Visit (Visit 0) * Willingness to be discontinued from current phosphate binder(s) and initiated on KRX-0502 (ferric citrate) * Willing and able to give informed consent * Willing and able to stay on a constant dose of Vitamin D (or its analogs) and Sensipar (cinacalcet) for the treatment period, if applicable. Exclusion Criteria: * Parathyroidectomy within six months prior to Screening Visit (Visit 0) * Actively symptomatic gastrointestinal bleeding or inflammatory bowel disease * Serum phosphorus levels \>10.0 mg/dL documented in all of the three monthly laboratories (done routinely in the dialysis unit) in the three months prior to the Screening Visit (Visit 0) * History of multiple drug allergies or intolerances * History of malignancy in the last five years (treated cervical or non-melanomatous skin cancer may be permitted if approved by CCC) * Previous intolerance to oral ferric citrate * Absolute requirement for oral iron therapy * Absolute requirement for Vitamin C (multivitamins \[Nephrocaps, Renaphro, etc.\] allowed) * Absolute requirement for calcium-, magnesium-, or aluminum-containing drugs with meals * Psychiatric disorder that interferes with the patient's ability to comply with the study protocol * Inability to tolerate oral drug intake * Planned surgery or hospitalization during the trial (scheduled outpatient access surgery allowed) * Any other medical condition that renders the patient unable to or unlikely to complete the trial or that would interfere with optimal participation in the trial or produce significant risk to the patient * Receipt of any investigational drug within 30 days of Screening Visit (Visit 0) * Inability to cooperate with study personnel or history of noncompliance * Unsuitable for this trial per Principal Investigator's clinical judgment