The present trial is conducted to further assess the efficacy by means of serial spirometry, safety and tolerability of three doses of aclidinium bromide administered twice a day compared to previously approved BID drug, formoterol 12 µg, and placebo in patients with moderate to severe chronic obstructive pulmonary disease (COPD).after 7 days on treatment. Every treatment period is 7-days long and there is a 5 to 7-days wash-out period in between them. The trial starts with a run in phase of 11 to 17-days duration and it ends up with a follow up contact 14-days after last treatment dose.