Does concomitant administration of sevelamer and calcium carbonate modify the control of phosphatemia?

There is no guideline regarding the concomitant or distant administration of sevelamer and calcium carbonate. Our aim was to determine whether serum phosphate varied when sevelamer and calcium carbonate were administered concomitantly in comparison to administration at separate meals. Fourteen chronic hemodialysis patients were enrolled in this cross-over, randomized trial. Each subject underwent two four-week study periods. During the "concomitant" period, subjects were instructed to take both sevelamer and calcium carbonate together at each meal, whereas in the "separate" period, they were required to take them at separate meals. The order of the "concomitant" and "separate" periods was randomized. Phosphate-binding agents were stopped for a one-week washout period before each study period. The total dose of sevelamer and calcium carbonate for each subject remained the same for the whole duration of the study and had been determined according to their usual dose of phosphate binders. Patients were instructed to keep their usual eating habits constant and a nutritionist evaluated the daily phosphate intake three times per week. Dialysis parameters were kept constant. Pre-dialysis serum phosphate, calcium, bicarbonate, and albumin were measured at the end of each week. The average daily dietary phosphate intake remained unchanged throughout the study. At the end of the two study periods there was no significant difference in serum phosphate (1.50 +/- 0.46 mmol/L in the "concomitant" period vs. 1.51 +/- 0.31 mmol/L in the "separate" period, P = 0.97), calcium (2.26 +/- 0.19 mmol/L in the "concomitant" period vs. 2.27 +/- 0.15 mmol/L in the "separate" period, P = 0.64), calcium x phosphate product (3.36 +/- 0.94 mmol(2)/L-2 in the "concomitant" period vs. 3.41 +/- 0.71 mmol(2)/L-2 in the "separate" period, P = 0.84) and bicarbonate levels (21.5 +/- 3.3 mmol/L for the "concomitant" period vs. 21.6 +/- 3.1 mmol/L for the "separate" period, P = 0.81). Our results show that simultaneous administration of calcium carbonate and sevelamer does not decrease phosphate-binding capacity. Hence, patients can choose to take their phosphate binders concomitantly or at separate meals, according to their preference.