Patients on hemodialysis tend to have chronic elevations in the level of phosphorus in the blood and a secondary increase in the iPTH level. This chronic elevation in iPTH can have adverse consequences, thus a variety of phosphate binders are given in an attempt to decrease the absorption of phosphorus present in the normal diet. Some preliminary studies have indicated that the iPTH level may change based on the amount of phosphorus present in a meal prior to any significant absorption of phosphorus. If this is true in hemodialysis patients, then the timing of the administration of phosphate binders in relation to the ingestion of meals needs to be considered

Drugs used will include three phosphate binders already approved and commonly used. Calcium acetate, aluminum hydroxide, and sevelamer (Renagel) will be given on separate occasions in conjunction with a high phosphorus meal. They will be given in standard doses used in the treatment of high phosphorus levels in hemodialysis patients.

The population targeted will included hemodialysis patients with elevated iPTH and phosphorus levels.

The patients will receive up to five separate meals. Four of these will be high phosphorus content meals and one will be a low phosphorus content meal. On up to three occasions with the high phosphorus content meals the patients will ingest one of the three phosphate binders. The meals will be ingested after a twelve-hour overnight fast. Labs will be drawn prior to meal ingestion and then at 15, 30, 60, 120 and 240-minute intervals. The labs will consist of iPTH, phosphorus, calcium, and glucose. A serum albumin level will be obtained with the initial specimen only. The patients will have an iPTH level of at least 200pg/ml and a serum phosphorus level of at least 4.0 mg/dl.

The primary outcome will be the change in the iPTH level in relation to the phosphorus content of the meals. Secondary outcomes will include the change in iPTH level in relation to the various phosphate binders being used.

Inclusion criteria:

• Patients 18 years of age or older
• Receiving treatment with hemodialysis for at least 90 days
• Serum iPTH levels greater than 200pg/ml
• Serum phosphorus levels greater than 4.0mg/dl