In chronic obstructive pulmonary disease (COPD), the airways of the lungs are narrowed or blocked. Bronchodilators are drugs usually delivered through inhalers which help open up the airways. Tiotropium is a type of bronchodilator drug known as a long-acting muscarinic antagonist (LAMA). For a long time tiotropium was the only available LAMA. More recently, a new LAMA called aclidinium has been approved for use in COPD. There are potentially important differences between these two medications that might have an impact on the treatment of COPD patients.