A selective muscarinic M2 receptor antagonist (IC50 = 6.1 nM in CHO-K1 cell membranes); selective for M2 over M1, M3, M4, and M5 receptors (IC50s = 92, 770, 260, and 217 nM, respectively); inhibits acetylcholine-induced reductions in isolated guinea pig tracheal tube contractions in vitro (1 μM); inhibits bradycardia and bronchoconstriction induced by acetylcholine in guinea pigs (ED50s = 38 and 81 nmol/kg, respectively); suppresses oxotremorine M-induced bladder overactivity in a rat model of spinal cord injury