• Changes in iPTH at 32 weeks.
• Safety and tolerability of cinacalcet at 32 weeks.

• "*Changes in iPTH at 32 weeks.
• *Safety and tolerability of cinacalcet at 32 weeks."

The purpose of this study is to evaluate the efficacy and safety of cinacalcet compared with placebo in patients with stage 3 and 4 Chronic Kidney Disease (CKD).

• Kidney Disease
• Chronic Kidney Disease

Inclusion Criteria: Chronic Kidney Disease patients not receiving dialysis with: - An iPTH greater than 100 pg/mL [10.6 pmol/L] for subjects with stage 3 CKD or greater than or equal to 160 pg/mL [17.0 pmol/L] for subjects with stage 4 CKD; - A serum calcium greater than 9.0 mg/dL [2.25 mmol/L]; - An estimated GFR less than or equal to 59 mL/min and greater than or equal to 15 mL/min. Exclusion Criteria: - Have an unstable medical condition, defined as having been hospitalized within 30 days before day 1, or otherwise unstable in the judgment of the investigator. - Experienced a myocardial infarction (MI) within 3 months before day 1. - Likely to initiate dialysis (in the opinion of the investigator) or are scheduled to undergo renal transplantation within 28 weeks after day 1. - Received active vitamin D therapy (i.e., 1-hydroxylated metabolites of vitamin D) for less than 30 days before day 1 or required a change in active vitamin D brand or dose level within 30 days before day 1 (for patients prescribed active vitamin D).