Umeclidinium bromide (CAS 869113-09-7) is a potent and long-acting antagonist of muscarinic acetylcholine receptors (mAChRs) displaying high affinity for subtypes M1 M5 with Ki values of 0 16 nM 0 15 nM 0 06 nM 0 05 nM and 0 13 nM respectively It selectively targets mAChRs without observable activity at unrelated receptors or channels such as / opioid receptors sodium channels or dopamine transporters In cell-based assays using CHO cells expressing recombinant human mAChRs umeclidinium inhibits acetylcholine-induced calcium flux with pA2 values between 9 6 and 10 6 for M1 M3 receptors In murine models it reverses acetylcholine-driven bronchoconstriction Umeclidinium bromide is broadly applied in research focused on pulmonary disease mechanisms and drug development