1) To evaluate the effectiveness of AST-120 (spherical carbon adsorbent) added to standard-of-care therapy in moderate to severe Chronic Kidney Disease (CKD), on time to first occurrence of any event of the triple composite outcome of initiation of dialysis, kidney transplant or doubling of serum creatinine (sCr) when compared with placebo; 2) To evaluate the safety and tolerability of long-term AST-120 therapy in patients with CKD; 3) To evaluate the effects of AST-120 versus placebo, on other measures of renal function.

Inclusion Criteria:

• Age 18 years or older
• Moderate to severe CKD, not anticipated to require dialysis or renal transplant within the next 6 months
• Patient survival expected to be no less than one year
• Serum creatinine in men >= 2.0 mg/dL (>= 177 µmol/L) and <= 5.0 mg/dL (<= 442 µmol/L), and in women >= 1.5 mg/dL (>= 133 µmol/L) and <= 5.0 mg/dL (<= 442 µmol/L) at Screening
• Urinary total protein to urinary total creatinine ratio must be >= 0.5 on a spot void at Screening
• Blood pressure <= 160/90 mmHg at both Screening and Baseline. In addition, blood pressure, if measured, must have been stable in hypertensive patients over the 3 months prior to Screening, with no more than 1 blood pressure reading > 160/90 mmHg
• In patients being treated for hypertension, they should be on a stable anti-hypertensive regimen

Exclusion Criteria:

• Obstructive or reversible cause of kidney disease
• Nephrotic syndrome defined as a ratio of urinary total protein to urinary creatinine of > 6.0 as measured on a spot void
• Adult polycystic kidney disease
• History of previous kidney transplant
• History of recent (within the past 6 months) accelerated or malignant hypertension
• Uncontrolled arrhythmia or severe cardiac disease within the past 6 months
• History of malabsorption, inflammatory bowel disease, hiatal hernia, active peptic ulcer, or severe GI dysmotility, not attributable to the use of a phosphate binder
• Received any investigational agent or participated in a clinical study within the previous 3 months
• Presence of any significant medical condition that might create an undue risk with study participation, or significantly confound the collection of safety and efficacy data in this study