A long-acting muscarinic receptor antagonist that binds equally to human muscarinic M1, M2, and M3 receptors (Kds = 0.04, 0.02, and 0.01 nM, respectively); dissociates slowly from M1 and M3 receptors, which are located on bronchial smooth muscle and submucosal glands, and more rapidly from M2 receptors (t 1/2 = 14.6 and 34.7 versus 3.6 hours, respectively).