Fosrenol and Phosphorus Balance - Lanthanum Carbonate

Positive phosphorus balance and hyperphosphatemia (increased serum phosphorus levels) are very common complications of people with advanced chronic kidney disease (i.e., stage 5 CKD), including chronic dialysis patients, and are associated with severe morbidity and increased mortality. Despite attempts to control serum phosphorus with dietary phosphorus restriction and the use of medicines that bind phosphorus in the gastrointestinal tract so that the phosphorus cannot be absorbed into the body( also called phosphate binders), chronic dialysis patients frequently remain hyperphosphatemic, particularly at the time when they commence each of their regular dialysis treatments. Fosrenol (lanthanum carbonate, manufactured by Shire Pharmaceuticals) is a gastrointestinal phosphate binder that appears to have the advantages of being safe, well tolerated and effective at binding phosphate. There are limited data on the magnitude of binding of phosphorus by Fosrenol in the human gastrointestinal tract of patients with chronic kidney disease. The specific aims for this proposal are as follows: 1. To quantify, under precisely controlled metabolic balance conditions, the increase in fecal excretion of dietary phosphorus that occurs when patients undergoing chronic peritoneal dialysis (CPD) ingest Fosrenol (lanthanum carbonate). 2. To examine a dose response relationship between Fosrenol treatment and fecal phosphorus excretion. The investigators will examine in CPD patients ingesting a constant phosphorus intake, how much additional phosphorus is excreted in the feces at three different dose levels of Fosrenol, 1.5, 3.0, and 4.5 g/day. 3. To examine how increased fecal phosphorus losses and more negative phosphorus balance caused by Fosrenol intake affects serum phosphorus and such hormonal regulators of phosphorus metabolism as serum parathyroid hormone (PTH), fibroblast growth factor-23, 25-hydroxycholecalciferol (25(OH)D3), 1,25-dihydroxycholecalciferol (1,25(OH)2D3) and fetuin-A. 4. To assess whether there is any effect of Fosrenol and increased intestinal phosphate binding on protein-nitrogen balance.