Secondary objectives are: Comparing both preparations with regard to the number of patients reaching serum phosphate levels < 1.76 mmol/L and the difference in serum phosphate levels between the first and last visit under each treatment. Furthermore, it is the aim of this study to evaluate the safety profile of OsvaRen® granules in comparison to OsvaRen® tablets. Especially serum calcium, magnesium, and PTH are of interest.