The primary objectives of this study are the following:

1. To demonstrate that AMG 223 will produce a statistically significant reduction in serum phosphorus compared with placebo over a 3 week treatment period in subjects with CKD receiving dialysis
2. To describe a dose response for AMG 223
3. To evaluate the safety and tolerability of AMG 223

Inclusion Criteria:

• Maintenance hemodialysis 3 times a week for at least 3 months prior to screening
• Single pool Kt/V at least 1.2 or urea reduction ratio at least 65%
• Serum phosphorus level of 3.5 to 6.5 mg/dL inclusive at screening
• No change(s) in type or dose of non-investigational phosphate binder(s) for at least 1 month prior to screening
• Serum albumin > 3.0 mg/dL at screening
• If applicable, an increase in serum phosphorus of greater than or equal to 1.5 mg/dL, and a serum phophorous level > 5.5 mg/dL and less than or equal to 10 mg/dl during the washout period
• If applicable, stable doses (defined as no change in dose for at least 1 month prior to screening) of Vitamin D replacement, calcimimetic agents, or bedtime calcium supplements
• Willingness to avoid intentional changes in diet such as fasting or dieting

Exclusion Criteria:

• Previous intolerance leading to discontinuation of polymer-based phosphate binder therapy
• History of noncompliance with phosphate binder therapy in the opinion of the investigator
• Anticipating or scheduled for a living related-donor kidney transplant, or a prior recipient of a kidney transplant
• Current use of antiarrhythmic or anti-seizure medication
• Active ethanol or drug dependence or abuse, excluding tobacco use
• A screening serum calcium (corrected for albumin) < 8.4 mg/dL
• History of bowel obstruction, swallowing disorders, severe gastrointestinal disorders, major gastrointestinal surgery, or gastric/duodenal ulcers within 6 months prior to screening
• Subject is pregnant, breast feeding, or is of child bearing potential and is not using adequate contraceptive precautions
• Subject is currently enrolled in or has not yet completed at least 30 days since ending other investigational device or drug trial(s)
• Subject has experienced a myocardial infarction or major surgery (excluding vascular access surgery) within 3 months prior to screening
• Clinical evidence of current malignancy and/or receiving systemic chemotherapy/radiotherapy with the exception of localized basal cell or squamous cell carcinoma of the skin and cervical intraepithelial neoplasia