Sevelamer worsens metabolic acidosis in hemodialysis patients

Sevelamer hydrochloride, a major phosphate binder for patients on maintenance hemodialysis (MHD) is associated with reduced serum bicarbonate concentration due to hydrochloric acid release in the gut and to the binding of short chain fatty acids in the large intestine. Since metabolic acidosis can be deleterious, a study was devised to compare the time course of serum bicarbonate concentration during treatment with sevelamer hydrochloride or calcium carbonate.

Sixteen well nourished patients on MHD who were in excellent clinical conditions and achieving target levels for blood pressure (BP) and hemoglobin (Hb), while on a protein intake of 1.1g/kg body weight (bw), were enrolled in the study. After a 2-week washout period, the patients were divided into two groups, each consisting of eight patients, and randomized either to 24 weeks of sevelamer followed by 24 weeks of calcium carbonate (group A) or to 24 weeks of calcium carbonate followed by 24 weeks of sevelamer (group B). Protein intake, n-protein catabolic rate (nPCR), serum concentrations of calcium, phosphate, calcium x phosphate (Ca x P) product, bicarbonate, intact parathyroid hormone (iPTH) and albumin were monitored. Time course changes in serum bicarbonate concentrations in relation to short and long dialytic intervals (48 vs. 72 hr) were also investigated.

Both sevelamer and calcium carbonate effectively controlled serum phosphate and the Ca x P product. During calcium carbonate treatment plasma phosphate concentrations were significantly below those of patients on sevelamer. Plasma bicarbonate concentration fell within target DOQI values during calcium carbonate administration both in group A and in group B, a goal which was not achieved under sevelamer administration. After a long dialytic interval in patients on sevelamer, serum bicarbonate concentration averaged 17.3 +/- 1.1 mEq/L, whereas it averaged 21.1 +/- 0.7 mEq/L in patients on calcium carbonate (p<0.01). Finally, a 24-week sevelamer administration caused a statistically significant (p<0.05) reduction (0.8 g/dL) in serum albumin concentration, without affecting iPTH. Taken together, these results indicate that sevelamer worsens metabolic acidosis, which needs to be corrected.