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 and quality of life.