Effects of Lanthanum Carbonate on Whole-Body Phosphorus and Calcium Balance in Adults With Chronic Kidney Disease and Normophosphatemia

RATIONALE & OBJECTIVE: Greater serum phosphorus is associated with cardiovascular disease in those with chronic kidney disease (CKD). However, the utility of phosphorus lowering in nondialysis-requiring CKD is not clear. The effects of noncalcium-based phosphate binders on phosphorus and calcium balance in nondialysis-requiring CKD are unknown. Our objective was to determine phosphorus and calcium balance in normophosphatemic adults with CKD 3b-4 after 12 weeks of treatment with lanthanum carbonate or placebo. STUDY DESIGN: Prospective, randomized, controlled, double-blind clinical trial. SETTING & PARTICIPANTS: A subset of 15 adults with CKD 3b-4 and serum phosphorus levels within normal limits who participated in a 12-week parallel-arm, randomized controlled trial of lanthanum carbonate compared with placebo on vascular function participated in this study extension. INTERVENTION: At the end of 12 weeks, the subset of participants consumed a controlled diet (1,000 mg/day phosphorus and 800 mg/day calcium) for 9 days and continued their randomly assigned study drug (N = 7 lanthanum carbonate, N = 8 placebo). Fasting morning blood samples and all stool and urine were collected during a 48-hour inpatient clinical research center stay at the end of the 9-day controlled diet period. OUTCOMES: Phosphorus and calcium balance (mg/d) were determined by values averaged over the 48 hours inpatient clinical research center admission. RESULTS: Mean age was 65 ± 8 (SD) years, and mean estimated glomerular filtration rate was 38 ± 14 (SD) mL/min/1.73m2. Whole-body phosphorus balance was lower with lanthanum carbonate compared with placebo (-131 ± 163 [SEM] vs 320 ± 141 mg/d, P = 0.05), as was calcium balance (-46 ± 115 [SEM] vs 410 ± 100 mg/d, P = 0.01), corresponding to lower intestinal absorption supported by the fecal calcium and phosphorus and net absorption results. Neither 24-hour urine calcium nor phosphorus output was significantly different between lanthanum carbonate and placebo, but 24-hour urine phosphorus output differed between lanthanum carbonate and placebo but was not significant (388 ± 60 vs 513 ± 56 mg/d, p=0.15). LIMITATIONS: Small sample size. CONCLUSIONS: Twelve weeks of treatment with the noncalcium-based phosphate binder, lanthanum carbonate, may reduce whole-body phosphorus balance as well as calcium balance among adults with stage 3b-4 CKD and normophosphatemia. Whether reduced phosphorus balance or calcium balance with lanthanum carbonate is associated with beneficial clinical outcomes in CKD warrants further investigation.