Study hypothesis: Nicotinamide inhibits gastrointestinal phosphate absorption and serum phosphate levels of dialysis patients in a dose dependent manner.

Inclusion Criteria:

• hemodialysis since 3 months or longer
• hemodialysis frequency 3 times weekly
• stable phosphate binder dose since one month at screening
• serum phosphate level < 2,42 mmol/l at screening
• serum phosphate level > 1,52 mmol/l after wash out phase
• stable treatment with vitamin D analogues since one month at screening

Exclusion Criteria:

• congestive heart failure
• acute bleeding complications
• acute myocardial infarction
• peptic ulcers
• serious liver damage
• poorly controlled diabetes
• severe visual impairment
• uncontrolled high blood pressure
• thrombocyte count < 120/nl
• difficulties in swallowing or dysphagia
• diminished intestinal motility, megacolon, pseudo- or mechanical obstruction
• gastroparesis