The treatment period starts with a 12-week, double-blind, placebo-controlled, randomized period followed by an open-label extension phase. In the double-blind phase, eligible patients are randomized (4:1 ratio) to receive either certolizumab pegol (CZP) or Placebo up to and including Week 10. The randomization will be stratified according to the three factors: concomitant use of methotrexate (MTX, Yes or No), prior anti-tumor necrosis factor (anti-TNF) use (Yes or No), and disease duration categories (\< 2 years or ≥ 2 years). From Week 12 all patients remaining in the study receive open-label CZP for a minimum 16 additional weeks until CZP is commercially available.
