The overall goal of this project is to define pharmacokinetic and pharmacodynamic properties of UroPhos-K. It will test the hypotheses that (a) UroPhos-K compared with rapid-release phosphate, has a greater overall phosphate bioavailability and blunted circadian fluctuation in serum and urinary phosphate, and (b) UroPhos-K at a specific low dose confers the same desired pharmacodynamic effects as two higher doses.