FGF23 Reduction : Efficacy of a New Phosphate Binder in CHronic Kidney Disease

The total length of the study is 14 weeks divided in 2 parts the first part is the screening period she will stay 1 to 2 weeks and the second period with the treatment with permanent dosage during 12 weeks.

During the screening visit (Vo) inclusion and non inclusion criteria will be checked and the patient consent will be collected. Biological analysis will be performed.

If the patient still eligible after the reception of biological results, he will be randomized and will received, either sevelamer carbonate, either placebo. The study treatment will be begun at the randomisation visit (V1) the dosage will be 2 tablets 3 times per day (corresponding to 4.8g/d sevelamer carbonate for patient taken active medication).

Patient will be seen every 2 weeks after the first visit (+/-5days) during 6 weeks (visit2/day15, visit3/day30, visit4/day45) and 12 weeks after the randomisation visit (visit5/day90). This visits will include biological analysis, compliance evaluation, adverse events report, concomitant treatments reports.

After the consent signature, all the adverse events will be collected until the end of the study for the patient (Visit5 or end of the study visit). Serious adverse events will be collected until 30 days after the date of the end of the study.

The same dosage of the study treatment will be followed during all the study period except if the phosphatemia (evaluated during one analysis) is found above the normal range planned by the protocol. In this case, the dosage adaptations will be :

* If during a visit the phosphatemia is above or equal to 0.8 mmol/l and superior to 0.5 mmol/l, the study treatment dosage need to be reduce to 2 tablets 3 times per day to 1 tablet 3 times per day. * If during the next blood punction, the phosphatemia still or equal to 0.8 mmol/l and superior to 0.5 mmol/l, the study treatment will be stopped and a "end of study" visit will be performed. * If during one study visit, the phosphatemia is above or equal to 0.5 mmol/l,the study treatment will be stopped immediately and a end of study visit will be performed.