ACR20 response rates were 62.5 % , 76.8 % , 77.6 % , and 28.6 % at Week 12 , and 61.1 % , 73.2 % , 71.8 % , and 24.7 % at Week 24 for CZP 100 , 200 , and 400 mg , and placebo groups , respectively , with statistical significance between each CZP group and placebo .