Darotropium is a muscarinic acetylcholine antagonist, developed by GlaxoSmithKline for the treatment of chronic obstructive pulmonary disease (COPD). Darotropium in combination with salmeterol was investigated in phase 2 clinical trial in COPD patients. The addition of darotropium to salmeterol in partially reversible COPD patients resulted in greater bronchodilation than salmeterol or tiotropium alone and was well tolerated. In a clinical trial of darotropium as monotherapy, all doses of the drug were well tolerated and demonstrated bronchodilatory activity. However, the rapid onset of bronchodilation was not sustained over 24 h, and GSK has discontinued the development of darotropium in favor of GSK573719, which has more favorable pharmacokinetics.