A long-term safety study of ferric citrate (KRX-0502) in renal failure patients who have completed study KRX-0502-304. Only patients who participated in the KRX-0502-304 trial may participate in this trial.

This study was an open-label, 48-week safety extension of Study KRX-0502-304 (Study 304), to evaluate the safety of long-term use of KRX-0502 in subjects with ESRD for up to 2 years of cumulative exposure. Subjects who completed the Safety Assessment Period (SAP) and, if eligible, the Efficacy Assessment Period (EAP) of Study 304, independent of their assigned treatment arm in the SAP or EAP of Study 304, were eligible for participation in this long-term safety extension study. No new subjects were permitted to enter this study.

Inclusion Criteria:

1. Males or non-pregnant, non-breast-feeding females who participated in the Safety Assessment Period (SAP), and if eligible, the Efficacy Assessment Period (EAP) of Study KRX-0502-304
2. Willing and able to give informed consent

Exclusion Criteria:

1. Subjects on KRX-0502 (ferric citrate) in KRX-0502-304 who were treatment failures in first period
2. Any subject in Study KRX-0502-304 SAP who early terminated from the trial
3. Any subject who participated in Study KRX-0502-304 but declined EAP
4. Actively symptomatic gastrointestinal bleeding or inflammatory bowel disease
5. History of malignancy in the last five years
6. Previous intolerance to KRX-0502 (ferric citrate)
7. Intolerance to oral iron-containing products
8. Absolute requirement for oral iron therapy
9. Absolute requirement for Vitamin C (multivitamins [Nephrocaps, Renaphro, etc.] allowed)
10. Absolute requirement for calcium-, magnesium-, or aluminum-containing drugs with meals
11. Inability to tolerate oral drug intake
12. Any other medical condition that rendered the subject unable to or unlikely to complete the trial or that would interfere with optimal participation in the trial or produce significant risk to the subject
13. Inability to cooperate with study personnel or history of noncompliance
14. Unsuitable for this trial per Principal Investigator's (PI) clinical judgment.