Stage 1 was a 24-week long open-label, randomized, active controlled, parallel-group evaluating the safety and efficacy of VELPHORO therapy in ESRD patients on dialysis. 1,055 patients on hemodialysis (HD) (N=968) and peritoneal dialysis (PD) (N=87) who were hyperphosphatemic (serum phosphorus ≥1.94 mmol/L) following a 2-4 week phosphate binder washout period, were randomized and received VELPHORO at a starting dose of 1,000 mg iron/day (N=707) or comparator drug (sevelamer carbonate, N=348) for 24 weeks. During the first 8 weeks, VELPHORO dose increases or decreases by steps of 500 mg iron/day every 2 weeks were permitted for efficacy (to achieve target serum phosphorus levels between 0.81 and 1.78 mmol/L) and tolerability reasons, to a minimum dose of 1,000 mg iron/day or maximum dose of 3,000 mg iron/day. VELPHORO was administered with food and the daily dose was divided across the largest meals of the day. After this 8-week dose titration period, subjects were continued on a stable dose of either VELPHORO or sevelamer carbonate for a further 4-week maintenance period. Dose titrations for tolerability reasons only were allowed during this period. At the end of 12 weeks, a secondary non-inferiority efficacy comparison of VELPHORO versus sevelamer carbonate with respect to change from baseline in serum phosphorus levels was performed. Subjects were continued on their study medication from Week 12 to Week 24, during which time dose titrations were allowed for both tolerability and efficacy reasons.