Buffering effects of calcium carbonate as clarified by sevelamer hydrochloride monotherapy

This study was undertaken to examine the necessity of taking into account the acid-base balance to ensure safe switching from calcium carbonate to sevelamer hydrochloride in hemodialysis patients. Forty-two hemodialysis patients were divided into two groups: the sevelamer hydrochloride therapy group (n = 18; "monotherapy group") and the combined calcium carbonate plus sevelamer hydrochloride therapy group (n = 24; "combined therapy group"). Observation was continued for six months. Subsequently, treatment with calcium carbonate was resumed in the monotherapy group at a dose level equal to that used before the start of study, and the combined therapy group continued to receive combined calcium carbonate + sevelamer hydrochloride therapy for another six months. The monotherapy group showed marked metabolic acidosis (HCO3- level from 20.2 +/- 2.4 mmol/L to 17.7 +/- 0.5 mmol/L). While the acidosis also became worse in the combined therapy group, the decrease in serum HCO3- level was smaller in this group than in the monotherapy group. The monotherapy group showed rapid recovery from acidosis following resumption of calcium carbonate administration (HCO3- level from 17.7 +/- 0.5 mmol/L to 20.6 +/- 0.7 mmol/L). We analyzed the cause of acidosis by the Stewart-Figge approach, and it was found to be attributable to the elevation of the serum Cl- level. The results suggest that treatment with calcium carbonate shows some buffering effects. Calcium carbonate acts as a potent alkalizing agent. We therefore consider it advisable to use sevelamer hydrochloride in combination with calcium carbonate in hemodialysis patients.