Aclidinium bromide is a novel, inhaled, long-acting antimuscarinic agent being developed by Almirall Prodesfarma SA and Forest Laboratories Inc as a once-daily treatment for COPD. In preclinical studies, aclidinium bromide demonstrated a comparable profile to tiotropium bromide, with a slightly quicker onset of action but shorter duration of action. Clinical trials have demonstrated an unquestionably interesting pharmacological profile characterized by a faster rate of onset of the smooth muscle relaxing activity than tiotropium bromide and a rapid plasma hydrolysis in human plasma to inactive metabolites that may account for its favorable cardiovascular safety profile. However, the disappointing efficacy results of the recent phase III trials have cast doubt on the real advantage of introducing this drug on the market. Discussions with the FDA concluded that more trials are needed to assess selected dosing regimens, including higher and/or more frequent doses. At the time of publication, further phase III trials with aclidinium bromide were ongoing, and the developing companies were also extending development to combinations of aclidinium bromide with formoterol or an undisclosed inhaled corticosteroid.