Selective M3 muscarinic receptor antagonist (pKi values are 8.52, 7.93, 7.90 and 7.78 for M3, M2, M1 and M4 receptors respectively). Displays higher affinity at ileal M3 receptors (pKi = 9.3) compared to oesophageal and tracheal M3 receptors (pKi values are 8.8 and 8.2 respectively). Inhibits gastrointestinal motility in vivo in the absence of cardiovascular effects.