Methoctramine is a selective antagonist of M2 muscarinic acetylcholine receptors (IC50 = 6.1 nM in CHO-K1 cell membranes).[1] It is selective for M2 over M1, M3, M4, and M5 receptors (IC50s = 92, 770, 260, and 217 nM, respectively).

In vitro, methoctramine inhibits acetylcholine-induced reductions in isolated guinea pig tracheal tube contractions when used at a concentration of 1 μM.[2]

In vivo, methoctramine inhibits bradycardia and bronchoconstriction induced by acetylcholinein guinea pigs with ED50 values of 38 and 81 nmol/kg, respectively. In a rat model of spinal cord injury, methoctramine suppresses bladder overactivity induced by the non-selective muscarinic acetylcholine receptor agonist oxotremorine M.[3]