The objective of this study is to see if KRX-0502 (ferric citrate) is safe and effective as a dietary phosphate binder in controlling and managing serum phosphorus levels in patients with end-stage renal disease (ESRD).

This is a multi-center, non-blinded, efficacy and tolerability trial in patients with ESRD on dialysis three times per week. Approximately 24 patients (approximately twelve diabetic patients and approximately twelve non-diabetic patients) in Israel will be initiated on KRX-0502 (ferric citrate). The study will consist of a two-week washout period immediately followed by a six-week treatment period in. Patients will be initiated on study drug over two to three weeks.

Inclusion Criteria:

1. Males and non-pregnant, non-lactating females
2. Age > 18 years
3. On thrice weekly hemodialysis for at least the previous three months prior to screening
4. Serum phosphorus levels ≥ 2.5 mg/dL and < 8.5 mg/dL at Screening Visit (Visit 0)
5. Serum phosphorus levels > 5.5 mg/dL at Study Drug Initiation Visit (Visit 3)
6. Taking 3 to 18 tablets/capsules/day of calcium acetate calcium carbonate, lanthanum carbonate, sevelamer (hydrochloride or carbonate), or any combination of these agents as reported by the patient at screening
7. Serum ferritin <1000micrograms/L and Transferrin Saturation (TSAT) <50%
8. Willing to be discontinued from current phosphate binder(s) and initiated on KRX-0502 (ferric citrate)
9. Willing and able to give informed consent

Exclusion Criteria:

1. Parathyroidectomy within six months prior to Screening Visit (Visit 0)
2. Actively symptomatic gastrointestinal bleeding and inflammatory bowel disease
3. Serum phosphorus levels >10.0 mg/dL documented in the three monthly laboratories (done routinely in the dialysis unit) in the three months prior to the Screening Visit (Visit 0)
4. History of multiple drug allergies
5. History of malignancy in the last five years (treated cervical or skin cancer may be permitted if approved by Keryx)
6. Previous intolerance to oral ferric citrate
7. Absolute requirement for oral iron therapy
8. Absolute requirement for Vitamin C (multivitamins [Centrum, Nephrocaps, Renaphro, etc.] allowed)
9. Absolute requirement for calcium, magnesium, or aluminum containing drugs with meals
10. Psychiatric disorder that interferes with the patient's ability to comply with the study protocol
11. Inability to tolerate oral drug intake
12. Planned surgery or hospitalization during the study (scheduled outpatient access surgery allowed)
13. Any other medical condition that renders the patient unable to or unlikely to complete the study or that would interfere with optimal participation in the study or produce significant risk to the patient
14. Receipt of any investigational drug within 30 days of randomization
15. Inability to cooperate with study personnel or history of noncompliance
16. Prior exposure to ferric citrate
17. Patients with hemochromatosis or Thalassemia

Patients selected from pool of dialysis patients at each clinic.